springboot2学习

springboot-梦开始的起点

前言、SpringBoot2课程介绍

  1. Spring Boot 2核心技术
  2. Spring Boot 2响应式编程

1、基础入门

1.1、Spring生态圈

1.1.1 Spring能做什么

Spring的能力
在这里插入图片描述

Spring的生态

覆盖了：

  • web开发
  • 数据访问
  • 安全控制
  • 分布式
  • 消息服务
  • 移动开发
  • 批处理
  • …

Spring5重大升级

  • 响应式编程

在这里插入图片描述

  • 内部源码设计

基于Java8的一些新特性，如：接口默认实现。重新设计源码架构。

为什么用SpringBoot

Spring Boot makes it easy to create stand-alone, production-grade Spring based Applications that you can “just run”.link

能快速创建出生产级别的Spring应用。

SpringBoot优点

  • Create stand-alone Spring applications

    • 创建独立Spring应用

  • Embed Tomcat, Jetty or Undertow directly (no need to deploy WAR files)

    • 内嵌web服务器

  • Provide opinionated ‘starter’ dependencies to simplify your build configuration

    • 自动starter依赖，简化构建配置

  • Automatically configure Spring and 3rd party libraries whenever possible

    • 自动配置Spring以及第三方功能

  • Provide production-ready features such as metrics, health checks, and externalized configuration

    • 提供生产级别的监控、健康检查及外部化配置

  • Absolutely no code generation and no requirement for XML configuration

    • 无代码生成、无需编写XML

  • SpringBoot是整合Spring技术栈的一站式框架

  • SpringBoot是简化Spring技术栈的快速开发脚手架

SpringBoot缺点

  • 人称版本帝，迭代快，需要时刻关注变化
  • 封装太深，内部原理复杂，不容易精通

1.1.2、SpringBoot的大时代背景

微服务

In short, the microservice architectural style is an approach to developing a single application as a suite of small services, each running in its own process and communicating with lightweight mechanisms, often an HTTP resource API. These services are built around business capabilities and independently deployable by fully automated deployment machinery. There is a bare minimum of centralized management of these services, which may be written in different programming languages and use different data storage technologies.——James Lewis and Martin Fowler (2014)

  • 微服务是一种架构风格
  • 一个应用拆分为一组小型服务
  • 每个服务运行在自己的进程内，也就是可独立部署和升级
  • 服务之间使用轻量级HTTP交互
  • 服务围绕业务功能拆分
  • 可以由全自动部署机制独立部署
  • 去中心化，服务自治。服务可以使用不同的语言、不同的存储技术

分布式
在这里插入图片描述

分布式的困难

  • 远程调用
  • 服务发现
  • 负载均衡
  • 服务容错
  • 配置管理
  • 服务监控
  • 链路追踪
  • 日志管理
  • 任务调度
  • …

分布式的解决

  • SpringBoot + SpringCloud

在这里插入图片描述

云原生

原生应用如何上云。 Cloud Native

上云的困难

  • 服务自愈
  • 弹性伸缩
  • 服务隔离
  • 自动化部署
  • 灰度发布
  • 流量治理
  • …

上云的解决

在这里插入图片描述

1.1.3、SpringBoot官方文档架构

官网文档架构
在这里插入图片描述

查看版本新特性
在这里插入图片描述

1.2、SpringBoot-HelloWorld

1.2.1、系统要求

  • Java 8
  • Maven 3.3+
  • IntelliJ IDEA 2019.1.2

1.2.2、Maven配置文件

新添内容：

<mirrors>
	<mirror>
		<id>nexus-aliyun</id>
		<mirrorOf>central</mirrorOf>
		<name>Nexus aliyun</name>
		<url>http://maven.aliyun.com/nexus/content/groups/public</url>
	</mirror>
</mirrors>

<profiles>
	<profile>
		<id>jdk-1.8</id>

		<activation>
			<activeByDefault>true</activeByDefault>
			<jdk>1.8</jdk>
		</activation>

		<properties>
			<maven.compiler.source>1.8</maven.compiler.source>
			<maven.compiler.target>1.8</maven.compiler.target>
			<maven.compiler.compilerVersion>1.8</maven.compiler.compilerVersion>
		</properties>
	</profile>
</profiles>

1.2.3、 具体步骤

需求：浏览发送/hello请求，响应 “Hello，Spring Boot 2”

创建maven工程
[1] 引入依赖

<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-parent</artifactId>
	<version>2.3.4.RELEASE</version>
</parent>

<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
</dependencies>

[2] 创建主程序

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MainApplication {

    public static void main(String[] args) {
        SpringApplication.run(MainApplication.class, args);
    }
}

[3] 编写业务

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {
    @RequestMapping("/hello")
    public String handle01(){
        return "Hello, Spring Boot 2!";
    }
}

[4] 运行&测试

  • 运行MainApplication类
  • 浏览器输入http://localhost:8888/hello，将会输出Hello, Spring Boot 2!。

[5] 注意

启动出现这个问题：

This application has no explicit mapping for /error, so you are seeing this

在这里插入图片描述

解决方法：Application启动类的位置不对.要将Application类放在最外侧,即包含所有子包
在这里插入图片描述
放在boot里面启动就会不行。

[6] 设置配置

maven工程的resource文件夹中创建application.properties文件。

# 设置端口号
server.port=8888

更多配置信息

[7] 打包部署

在pom.xml添加

<build>
	<plugins>
		<plugin>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-maven-plugin</artifactId>
		</plugin>
	</plugins>
</build>

在IDEA的Maven插件上点击运行 clean 、package，把helloworld工程项目的打包成jar包。
在这里插入图片描述

打包好的jar包被生成在helloworld工程项目的target文件夹内。

用cmd运行java -jar boot-01-helloworld-1.0-SNAPSHOT.jar，既可以运行helloworld工程项目。

将jar包直接在目标服务器执行即可。

1.3、SpringBoot-依赖管理特性

  • 父项目做依赖管理
依赖管理
<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-parent</artifactId>
	<version>2.3.4.RELEASE</version>
</parent>

上面项目的父项目如下：
<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-dependencies</artifactId>
	<version>2.3.4.RELEASE</version>
</parent>

它几乎声明了所有开发中常用的依赖的版本号，自动版本仲裁机制
  • 开发导入starter场景启动器
    1. 见到很多 spring-boot-starter-* ： *就某种场景
    2. 只要引入starter，这个场景的所有常规需要的依赖我们都自动引入
    3. 更多SpringBoot所有支持的场景
    4. 见到的 *-spring-boot-starter： 第三方为我们提供的简化开发的场景启动器。
所有场景启动器最底层的依赖
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter</artifactId>
	<version>2.3.4.RELEASE</version>
	<scope>compile</scope>
</dependency>

  • 无需关注版本号，自动版本仲裁

    1. 引入依赖默认都可以不写版本
    2. 引入非版本仲裁的jar，要写版本号。

  • 可以修改默认版本号

    1. 查看spring-boot-dependencies里面规定当前依赖的版本 用的 key。
    2. 在当前项目里面重写配置，如下面的代码。
<properties>
	<mysql.version>5.1.43</mysql.version>
</properties>

IDEA快捷键：

  • ctrl + shift + alt + U：以图的方式显示项目中依赖之间的关系。
  • alt + ins：相当于Eclipse的 Ctrl + N，创建新类，新包等。

1.4、SpringBoot-自动配置特性

  • 自动配好Tomcat
    • 引入Tomcat依赖。
    • 配置Tomcat
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-tomcat</artifactId>
	<version>2.3.4.RELEASE</version>
	<scope>compile</scope>
</dependency>

  • 自动配好SpringMVC

    • 引入SpringMVC全套组件
    • 自动配好SpringMVC常用组件（功能）

  • 自动配好Web常见功能，如：字符编码问题

    • SpringBoot帮我们配置好了所有web开发的常见场景
public static void main(String[] args) {
    //1、返回我们IOC容器
    ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args);

    //2、查看容器里面的组件
    String[] names = run.getBeanDefinitionNames();
    for (String name : names) {
        System.out.println(name);
    }
}
  • 默认的包结构
    • 主程序所在包及其下面的所有子包里面的组件都会被默认扫描进来
    • 无需以前的包扫描配置
    • 想要改变扫描路径
      • @SpringBootApplication(scanBasePackages=“com.lun”)
      • @ComponentScan 指定扫描路径
@SpringBootApplication
等同于
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan("com.lun")

  • 各种配置拥有默认值

    • 默认配置最终都是映射到某个类上，如：MultipartProperties
    • 配置文件的值最终会绑定每个类上，这个类会在容器中创建对象

  • 按需加载所有自动配置项

    • 非常多的starter
    • 引入了哪些场景这个场景的自动配置才会开启
    • SpringBoot所有的自动配置功能都在 spring-boot-autoconfigure 包里面

  • …

1.5、底层注解-@Configuration详解

  • 基本使用
    • Full模式与Lite模式
    • 示例
/**
 * 1、配置类里面使用@Bean标注在方法上给容器注册组件，默认也是单实例的
 * 2、配置类本身也是组件
 * 3、proxyBeanMethods：代理bean的方法
 *      Full(proxyBeanMethods = true)（保证每个@Bean方法被调用多少次返回的组件都是单实例的）（默认）
 *      Lite(proxyBeanMethods = false)（每个@Bean方法被调用多少次返回的组件都是新创建的）
 */
@Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
public class MyConfig {

    /**
     * Full:外部无论对配置类中的这个组件注册方法调用多少次获取的都是之前注册容器中的单实例对象
     * @return
     */
    @Bean //给容器中添加组件。以方法名作为组件的id。返回类型就是组件类型。返回的值，就是组件在容器中的实例
    public User user01(){
        User zhangsan = new User("zhangsan", 18);
        //user组件依赖了Pet组件
        zhangsan.setPet(tomcatPet());
        return zhangsan;
    }

    @Bean("tom")
    public Pet tomcatPet(){
        return new Pet("tomcat");
    }
}

@Configuration测试代码如下:

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan("com.atguigu.boot")
public class MainApplication {

    public static void main(String[] args) {
    //1、返回我们IOC容器
        ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args);

    //2、查看容器里面的组件
        String[] names = run.getBeanDefinitionNames();
        for (String name : names) {
            System.out.println(name);
        }

    //3、从容器中获取组件
        Pet tom01 = run.getBean("tom", Pet.class);
        Pet tom02 = run.getBean("tom", Pet.class);
        System.out.println("组件："+(tom01 == tom02));

    //4、com.atguigu.boot.config.MyConfig$$EnhancerBySpringCGLIB$$51f1e1ca@1654a892
        MyConfig bean = run.getBean(MyConfig.class);
        System.out.println(bean);

    //如果@Configuration(proxyBeanMethods = true)代理对象调用方法。SpringBoot总会检查这个组件是否在容器中有。
        //保持组件单实例
        User user = bean.user01();
        User user1 = bean.user01();
        System.out.println(user == user1);

        User user01 = run.getBean("user01", User.class);
        Pet tom = run.getBean("tom", Pet.class);

        System.out.println("用户的宠物："+(user01.getPet() == tom));
    }
}
  • 最佳实战
    • 配置 类组件之间无依赖关系用Lite模式加速容器启动过程，减少判断
    • 配置 类组件之间有依赖关系，方法会被调用得到之前单实例组件，用Full模式（默认）

lite 英 [laɪt] 美 [laɪt]
adj. 低热量的，清淡的(light的一种拼写方法);类似…的劣质品

IDEA快捷键：

  • Alt + Ins:生成getter，setter、构造器等代码。
  • Ctrl + Alt + B:查看类的具体实现代码。

1.6、底层注解-@Import导入组件

@Bean、@Component、@Controller、@Service、@Repository，它们是Spring的基本标签，在Spring Boot中并未改变它们原来的功能。

@ComponentScan 在1.4、SpringBoot-自动配置特性有用例。

@Import({User.class, DBHelper.class})给容器中自动创建出这两个类型的组件、默认组件的名字就是全类名

@Import({User.class, DBHelper.class})
@Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
public class MyConfig {
}

测试类：


//1、返回我们IOC容器
ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args);

//...

//5、获取组件
String[] beanNamesForType = run.getBeanNamesForType(User.class);

for (String s : beanNamesForType) {
    System.out.println(s);
}

DBHelper bean1 = run.getBean(DBHelper.class);
System.out.println(bean1);

1.7、底层注解-@Conditional条件装配

条件装配：满足Conditional指定的条件，则进行组件注入

在这里插入图片描述

用@ConditionalOnMissingBean举例说明

@Configuration(proxyBeanMethods = false)
@ConditionalOnMissingBean(name = "tom")//没有tom名字的Bean时，MyConfig类的Bean才能生效。
public class MyConfig {

    @Bean
    public User user01(){
        User zhangsan = new User("zhangsan", 18);
        zhangsan.setPet(tomcatPet());
        return zhangsan;
    }

    @Bean("tom22")
    public Pet tomcatPet(){
        return new Pet("tomcat");
    }
}

public static void main(String[] args) {
    //1、返回我们IOC容器
    ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args);

    //2、查看容器里面的组件
    String[] names = run.getBeanDefinitionNames();
    for (String name : names) {
        System.out.println(name);
    }

    boolean tom = run.containsBean("tom");
    System.out.println("容器中Tom组件："+tom);//false

    boolean user01 = run.containsBean("user01");
    System.out.println("容器中user01组件："+user01);//true

    boolean tom22 = run.containsBean("tom22");
    System.out.println("容器中tom22组件："+tom22);//true

}

1.8、底层注解-@ImportResource导入Spring配置文件

比如，公司使用bean.xml文件生成配置bean，然而你为了省事，想继续复用bean.xml，@ImportResource粉墨登场。

bean.xml：

<?xml version="1.0" encoding="UTF-8"?>
<beans ...">

    <bean id="haha" class="com.lun.boot.bean.User">
        <property name="name" value="zhangsan"></property>
        <property name="age" value="18"></property>
    </bean>

    <bean id="hehe" class="com.lun.boot.bean.Pet">
        <property name="name" value="tomcat"></property>
    </bean>
</beans>

使用方法：

@ImportResource("classpath:beans.xml")
public class MyConfig {
...
}

测试类：

public static void main(String[] args) {
    //1、返回我们IOC容器
    ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args);

	boolean haha = run.containsBean("haha");
	boolean hehe = run.containsBean("hehe");
	System.out.println("haha："+haha);//true
	System.out.println("hehe："+hehe);//true
}

1.9、底层注解-@ConfigurationProperties配置绑定

如何使用Java读取到properties文件中的内容，并且把它封装到JavaBean中，以供随时使用

传统方法：

public class getProperties {
     public static void main(String[] args) throws FileNotFoundException, IOException {
         Properties pps = new Properties();
         pps.load(new FileInputStream("a.properties"));
         Enumeration enum1 = pps.propertyNames();//得到配置文件的名字
         while(enum1.hasMoreElements()) {
             String strKey = (String) enum1.nextElement();
             String strValue = pps.getProperty(strKey);
             System.out.println(strKey + "=" + strValue);
             //封装到JavaBean。
         }
     }
 }

Spring Boot一种配置绑定：

@ConfigurationProperties + @Component

假设有配置文件application.properties

mycar.brand=BYD
mycar.price=100000

只有在容器中的组件，才会拥有SpringBoot提供的强大功能

@Component
@ConfigurationProperties(prefix = "mycar")
public class Car {
...
}

Spring Boot另一种配置绑定：

@EnableConfigurationProperties + @ConfigurationProperties

  1. 开启Car配置绑定功能
  2. 把这个Car这个组件自动注册到容器中
@EnableConfigurationProperties(Car.class)
public class MyConfig {
...
}

@ConfigurationProperties(prefix = "mycar")
public class Car {
...
}

1.10、自动配置【源码分析】-自动包规则原理

Spring Boot应用的启动类：

@SpringBootApplication
public class MainApplication {

    public static void main(String[] args) {
        SpringApplication.run(MainApplication.class, args);
    }

}

分析下@SpringBootApplication

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
    ...
}

重点分析@SpringBootConfiguration，@EnableAutoConfiguration，@ComponentScan。

@SpringBootConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
    @AliasFor(
        annotation = Configuration.class
    )
    boolean proxyBeanMethods() default true;
}

@Configuration代表当前是一个配置类。

@ComponentScan

指定扫描哪些Spring注解。

@ComponentScan 在1.4、SpringBoot-自动配置特性有用例。

@EnableAutoConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

    Class<?>[] exclude() default {};

    String[] excludeName() default {};
}

重点分析@AutoConfigurationPackage，@Import(AutoConfigurationImportSelector.class)。

@AutoConfigurationPackage

标签名直译为：自动配置包，指定了默认的包规则。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)//给容器中导入一个组件
public @interface AutoConfigurationPackage {
    String[] basePackages() default {};

    Class<?>[] basePackageClasses() default {};
}
  1. 利用Registrar给容器中导入一系列组件
  2. 将指定的一个包下的所有组件导入进MainApplication所在包下。

1.11、自动配置【源码分析】-初始加载自动配置类

@Import(AutoConfigurationImportSelector.class)

  1. 利用getAutoConfigurationEntry(annotationMetadata);给容器中批量导入一些组件
  2. 调用List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes)获取到所有需要导入到容器中的配置类
  3. 利用工厂加载 Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader);得到所有的组件
  4. 从META-INF/spring.factories位置来加载一个文件。
    • 默认扫描我们当前系统里面所有META-INF/spring.factories位置的文件
    • spring-boot-autoconfigure-2.3.4.RELEASE.jar包里面也有META-INF/spring.factories

在这里插入图片描述

# 文件里面写死了spring-boot一启动就要给容器中加载的所有配置类
# spring-boot-autoconfigure-2.3.4.RELEASE.jar/META-INF/spring.factories
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
...

虽然我们127个场景的所有自动配置启动的时候默认全部加载，但是xxxxAutoConfiguration按照条件装配规则（@Conditional），最终会按需配置。

如AopAutoConfiguration类：

@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnProperty(
    prefix = "spring.aop",
    name = "auto",
    havingValue = "true",
    matchIfMissing = true
)
public class AopAutoConfiguration {
    public AopAutoConfiguration() {
    }
	...
}

1.12、自动配置【源码分析】-自动配置流程

以DispatcherServletAutoConfiguration的内部类DispatcherServletConfiguration为例子:

@Bean
@ConditionalOnBean(MultipartResolver.class)  //容器中有这个类型组件
@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME) //容器中没有这个名字 multipartResolver 的组件
public MultipartResolver multipartResolver(MultipartResolver resolver) {
	//给@Bean标注的方法传入了对象参数，这个参数的值就会从容器中找。
	//SpringMVC multipartResolver。防止有些用户配置的文件上传解析器不符合规范
	// Detect if the user has created a MultipartResolver but named it incorrectly
	return resolver;//给容器中加入了文件上传解析器；
}

SpringBoot默认会在底层配好所有的组件，但是如果用户自己配置了以用户的优先。

总结：

  • SpringBoot先加载所有的自动配置类 xxxxxAutoConfiguration
  • 每个自动配置类按照条件进行生效，默认都会绑定配置文件指定的值。（xxxxProperties里面读取，xxxProperties和配置文件进行了绑定）
  • 生效的配置类就会给容器中装配很多组件
  • 只要容器中有这些组件，相当于这些功能就有了
  • 定制化配置
    • 用户直接自己@Bean替换底层的组件
    • 用户去看这个组件是获取的配置文件什么值就去修改。

xxxxxAutoConfiguration —> 组件 —> xxxxProperties里面拿值 ----> application.properties

1.13、最佳实践-SpringBoot应用如何编写

  • 引入场景依赖
  • 查看自动配置了哪些（选做）
    • 自己分析，引入场景对应的自动配置一般都生效了
    • 配置文件中debug=true开启自动配置报告。
      • Negative（不生效）
      • Positive（生效）
  • 是否需要修改
    • 参照文档修改配置项
      • 官方文档
      • 自己分析。xxxxProperties绑定了配置文件的哪些。
    • 自定义加入或者替换组件
      • @Bean、@Component…
    • 自定义器 XXXXXCustomizer；
    • …

1.14、最佳实践-Lombok简化开发

Lombok用标签方式代替构造器、getter/setter、toString()等鸡肋代码。

spring boot已经管理Lombok。引入依赖：

 <dependency>
     <groupId>org.projectlombok</groupId>
     <artifactId>lombok</artifactId>
</dependency>

IDEA中File->Settings->Plugins，搜索安装Lombok插件。

@NoArgsConstructor
//@AllArgsConstructor
@Data
@ToString
@EqualsAndHashCode
public class User {

    private String name;
    private Integer age;

    private Pet pet;

    public User(String name,Integer age){
        this.name = name;
        this.age = age;
    }
}

简化日志开发

@Slf4j
@RestController
public class HelloController {
    @RequestMapping("/hello")
    public String handle01(@RequestParam("name") String name){
        log.info("请求进来了....");
        return "Hello, Spring Boot 2!"+"你好："+name;
    }
}

1.15、最佳实践-dev-tools

Spring Boot includes an additional set of tools that can make the application development experience a little more pleasant. The spring-boot-devtools module can be included in any project to provide additional development-time features.——link

Applications that use spring-boot-devtools automatically restart whenever files on the classpath change. This can be a useful feature when working in an IDE, as it gives a very fast feedback loop for code changes. By default, any entry on the classpath that points to a directory is monitored for changes. Note that certain resources, such as static assets and view templates, do not need to restart the application.——link

Triggering a restart

As DevTools monitors classpath resources, the only way to trigger a restart is to update the classpath. The way in which you cause the classpath to be updated depends on the IDE that you are using:

  • In Eclipse, saving a modified file causes the classpath to be updated and triggers a restart.
  • In IntelliJ IDEA, building the project (Build -> Build Project)(shortcut: Ctrl+F9) has the same effect.

添加依赖：

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-devtools</artifactId>
        <optional>true</optional>
    </dependency>
</dependencies>

在IDEA中，项目或者页面修改以后：Ctrl+F9。

1.16、最佳实践-Spring Initailizr

Spring Initailizr是创建Spring Boot工程向导。

在IDEA中，菜单栏New -> Project -> Spring Initailizr。

1.17、配置文件-yaml的用法

同以前的properties用法

YAML 是 “YAML Ain’t Markup Language”（YAML 不是一种标记语言）的递归缩写。在开发的这种语言时，YAML 的意思其实是：“Yet Another Markup Language”（仍是一种标记语言）。

非常适合用来做以数据为中心的配置文件。

1.17.1 、基本语法

  • key: value；kv之间有空格
  • 大小写敏感
  • 使用缩进表示层级关系
  • 缩进不允许使用tab，只允许空格
  • 缩进的空格数不重要，只要相同层级的元素左对齐即可
  • '#'表示注释
  • 字符串无需加引号，如果要加，单引号’'、双引号""表示字符串内容会被 转义、不转义

1.17.2、数据类型

  • 字面量：单个的、不可再分的值。date、boolean、string、number、null
k: v
  • 对象：键值对的集合。map、hash、set、object
#行内写法：  

k: {k1:v1,k2:v2,k3:v3}

#或

k: 
  k1: v1
  k2: v2
  k3: v3
  • 数组：一组按次序排列的值。array、list、queue
#行内写法：  

k: [v1,v2,v3]

#或者

k:
 - v1
 - v2
 - v3

1.17.3、实例

@Data
public class Person {
    private String userName;
    private Boolean boss;
    private Date birth;
    private Integer age;
    private Pet pet;
    private String[] interests;
    private List<String> animal;
    private Map<String, Object> score;
    private Set<Double> salarys;
    private Map<String, List<Pet>> allPets;
}

@Data
public class Pet {
    private String name;
    private Double weight;
}

用yaml表示以上对象

person:
#  userName: "zhangsan \n 李四"
  # 单引号会将 \n 作为字符串输出  双引号会将 \n 作为换行输出
  # 双引号不会转义（不会改变原有转义字符的作用：比如：\n还是表示换行），单引号会转义
  boss: true
  birth: 2019/12/9
  age: 18
  interests:
    - 篮球
    - 足球
    - 18
#  interests: [篮球,足球,18]  行内写法
  animal:
    - 阿猫
    - 阿狗
#  animal: {阿猫,阿狗}
  score:
    english: 80
    math: 100
#  score: {english:80,math:100}
  salarys:
    - 9999.98
    - 9999.99
#  salarys: {9999.98,9999.99}
  pet:
    name: 阿狗
    weight: 99.99
  allPets:
    sick:
      - {name: 阿猫,weight: 99.99}
      - name: 阿狗
        weight: 55.455
      - name: 阿虫
        weight: 88.88
    health:
      - {name: 阿花,weight: 199.99}
      - {name: 阿明,weight: 199.99}
#    health: [{name: 阿花,weight: 199.99},{name: 阿明,weight: 199.99}]
  user-name: zhangsan

1.18、配置文件-自定义类绑定的配置提示

You can easily generate your own configuration metadata file from items annotated with @ConfigurationProperties by using the spring-boot-configuration-processor jar. The jar includes a Java annotation processor which is invoked as your project is compiled.——link

自定义的类和配置文件绑定一般没有提示。若要提示，添加如下依赖：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-configuration-processor</artifactId>
    <optional>true</optional>
</dependency>

<!-- 下面插件作用是工程打包时，不将spring-boot-configuration-processor打进包内，让其只在编码的时候有用 -->
<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <configuration>
                <excludes>
                    <exclude>
                        <groupId>org.springframework.boot</groupId>
                        <artifactId>spring-boot-configuration-processor</artifactId>
                    </exclude>
                </excludes>
            </configuration>
        </plugin>
    </plugins>
</build>

2、web场景

2.1、web开发简介

Spring Boot provides auto-configuration for Spring MVC that works well with most applications.(大多场景我们都无需自定义配置)

The auto-configuration adds the following features on top of Spring’s defaults:

  • Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.

    • 内容协商视图解析器和BeanName视图解析器

  • Support for serving static resources, including support for WebJars (covered later in this document)).

    • 静态资源（包括webjars）

  • Automatic registration of Converter, GenericConverter, and Formatter beans.

    • 自动注册 Converter，GenericConverter，Formatter

  • Support for HttpMessageConverters (covered later in this document).

    • 支持 HttpMessageConverters （后来我们配合内容协商理解原理）

  • Automatic registration of MessageCodesResolver (covered later in this document).

    • 自动注册 MessageCodesResolver （国际化用）

  • Static index.html support.

    • 静态index.html 页支持

  • Custom Favicon support (covered later in this document).

    • 自定义 Favicon

  • Automatic use of a ConfigurableWebBindingInitializer bean (covered later in this document).

    • 自动使用 ConfigurableWebBindingInitializer ，（DataBinder负责将请求数据绑定到JavaBean上）

If you want to keep those Spring Boot MVC customizations and make more MVC customizations (interceptors, formatters, view controllers, and other features), you can add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc.

不用@EnableWebMvc注解。使用 @Configuration + WebMvcConfigurer 自定义规则

If you want to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, and still keep the Spring Boot MVC customizations, you can declare a bean of type WebMvcRegistrations and use it to provide custom instances of those components.

声明 WebMvcRegistrations 改变默认底层组件

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc, or alternatively add your own @Configuration-annotated DelegatingWebMvcConfiguration as described in the Javadoc of @EnableWebMvc.

使用 @EnableWebMvc+@Configuration+DelegatingWebMvcConfiguration 全面接管SpringMVC

2.2、静态资源规则与定制化

2.2.1、静态资源目录

只要静态资源放在类路径下： called /static (or /public or /resources or /META-INF/resources)

访问 ： 当前项目根路径/ + 静态资源名

原理： 静态映射/**。

请求进来，先去找Controller看能不能处理。不能处理的所有请求又都交给静态资源处理器。静态资源也找不到则响应404页面。

也可以改变默认的静态资源路径，/static，/public,/resources, /META-INF/resources失效

resources:
  static-locations: [classpath:/haha/]

2.2.1、静态资源访问前缀

spring:
  mvc:
    static-path-pattern: /res/**

当前项目 + static-path-pattern + 静态资源名 = 静态资源文件夹下找

2.2.2、webjar

可用jar方式添加css，js等资源文件，

https://www.webjars.org/

例如，添加jquery

<dependency>
    <groupId>org.webjars</groupId>
    <artifactId>jquery</artifactId>
    <version>3.5.1</version>
</dependency>

访问地址：http://localhost:8080/webjars/jquery/3.5.1/jquery.js 后面地址要按照依赖里面的包路径。

2.3、welcome与favicon功能

官方文档

2.3.1、欢迎页支持

  • 静态资源路径下 index.html。

    • 可以配置静态资源路径
    • 但是不可以配置静态资源的访问前缀。否则导致 index.html不能被默认访问
spring:
#  mvc:
#    static-path-pattern: /res/**   这个会导致welcome page功能失效
  resources:
    static-locations: [classpath:/haha/]
  • controller能处理/index。

2.3.2、自定义Favicon

指网页标签上的小图标。

favicon.ico 放在静态资源目录下即可。

spring:
#  mvc:
#    static-path-pattern: /res/**   这个会导致 Favicon 功能失效

2.4、【源码分析】-静态资源原理

  • SpringBoot启动默认加载 xxxAutoConfiguration 类（自动配置类）
  • SpringMVC功能的自动配置类WebMvcAutoConfiguration，生效
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
    ...
}
  • 给容器中配置的内容：
    • 配置文件的相关属性的绑定：WebMvcProperties==spring.mvc、ResourceProperties==spring.resources
@Configuration(proxyBeanMethods = false)
@Import(EnableWebMvcConfiguration.class)
@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
@Order(0)
public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {
    ...
}

2.4.1、配置类只有一个有参构造器

有参构造器所有参数的值都会从容器中确定
public WebMvcAutoConfigurationAdapter(WebProperties webProperties, WebMvcProperties mvcProperties,
		ListableBeanFactory beanFactory, ObjectProvider<HttpMessageConverters> messageConvertersProvider,
		ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider,
		ObjectProvider<DispatcherServletPath> dispatcherServletPath,
		ObjectProvider<ServletRegistrationBean<?>> servletRegistrations) {
	this.mvcProperties = mvcProperties;
	this.beanFactory = beanFactory;
	this.messageConvertersProvider = messageConvertersProvider;
	this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider.getIfAvailable();
	this.dispatcherServletPath = dispatcherServletPath;
	this.servletRegistrations = servletRegistrations;
	this.mvcProperties.checkConfiguration();
}
  • ResourceProperties resourceProperties；获取和spring.resources绑定的所有的值的对象
  • WebMvcProperties mvcProperties 获取和spring.mvc绑定的所有的值的对象
  • ListableBeanFactory beanFactory Spring的beanFactory
  • HttpMessageConverters 找到所有的HttpMessageConverters
  • ResourceHandlerRegistrationCustomizer 找到 资源处理器的自定义器。
  • DispatcherServletPath
  • ServletRegistrationBean 给应用注册Servlet、Filter…

2.4.2、资源处理的默认规则

...
public class WebMvcAutoConfiguration {
    ...
	public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {
        ...
		@Override
		protected void addResourceHandlers(ResourceHandlerRegistry registry) {
			super.addResourceHandlers(registry);
			if (!this.resourceProperties.isAddMappings()) {
				logger.debug("Default resource handling disabled");
				return;
			}
			ServletContext servletContext = getServletContext();
			addResourceHandler(registry, "/webjars/**", "classpath:/META-INF/resources/webjars/");
			addResourceHandler(registry, this.mvcProperties.getStaticPathPattern(), (registration) -> {
				registration.addResourceLocations(this.resourceProperties.getStaticLocations());
				if (servletContext != null) {
					registration.addResourceLocations(new ServletContextResource(servletContext, SERVLET_LOCATION));
				}
			});
		}
        ...
        
    }
    ...
}

根据上述代码，我们可以通过配置禁止所有静态资源规则。

spring:
  resources:
    add-mappings: false   #禁用所有静态资源规则

静态资源规则：

@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties {

    private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
            "classpath:/resources/", "classpath:/static/", "classpath:/public/" };

    /**
     * Locations of static resources. Defaults to classpath:[/META-INF/resources/,
     * /resources/, /static/, /public/].
     */
    private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;
    ...
}

2.4.3、欢迎页的处理规则

...
public class WebMvcAutoConfiguration {
    ...
	public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {
        ...
		@Bean
		public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext,
				FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
			WelcomePageHandlerMapping welcomePageHandlerMapping = new WelcomePageHandlerMapping(
					new TemplateAvailabilityProviders(applicationContext), applicationContext, getWelcomePage(),
					this.mvcProperties.getStaticPathPattern());
			welcomePageHandlerMapping.setInterceptors(getInterceptors(mvcConversionService, mvcResourceUrlProvider));
			welcomePageHandlerMapping.setCorsConfigurations(getCorsConfigurations());
			return welcomePageHandlerMapping;
		}

WelcomePageHandlerMapping的构造方法如下：

WelcomePageHandlerMapping(TemplateAvailabilityProviders templateAvailabilityProviders,
                          ApplicationContext applicationContext, Resource welcomePage, String staticPathPattern) {
    if (welcomePage != null && "/**".equals(staticPathPattern)) {
        //要用欢迎页功能，必须是/**
        logger.info("Adding welcome page: " + welcomePage);
        setRootViewName("forward:index.html");
    }
    else if (welcomeTemplateExists(templateAvailabilityProviders, applicationContext)) {
        //调用Controller /index
        logger.info("Adding welcome page template: index");
        setRootViewName("index");
    }
}

这构造方法内的代码也解释了web场景-welcome与favicon功能中配置static-path-pattern了，welcome页面和小图标失效的问题。

2.5、请求处理-【源码分析】-Rest映射及源码解析

2.5.1、 请求映射

  • @xxxMapping;

    • @GetMapping
    • @PostMapping
    • @PutMapping
    • @DeleteMapping

  • Rest风格支持（使用HTTP请求方式动词来表示对资源的操作）

    • 以前：
      • /getUser 获取用户
      • /deleteUser 删除用户
      • /editUser 修改用户
      • /saveUser保存用户
    • 现在： /user
      • GET-获取用户
      • DELETE-删除用户
      • PUT-修改用户
      • POST-保存用户
    • 核心Filter；HiddenHttpMethodFilter

  • 用法

    • 开启页面表单的Rest功能
    • 页面 form的属性method=post，隐藏域 _method=put、delete等（如果直接get或post，无需隐藏域）
    • 编写请求映射
spring:
  mvc:
    hiddenmethod:
      filter:
        enabled: true   #开启页面表单的Rest功能

<form action="/user" method="get">
    <input value="REST-GET提交" type="submit" />
</form>

<form action="/user" method="post">
    <input value="REST-POST提交" type="submit" />
</form>

<form action="/user" method="post">
    <input name="_method" type="hidden" value="DELETE"/>
    <input value="REST-DELETE 提交" type="submit"/>
</form>

<form action="/user" method="post">
    <input name="_method" type="hidden" value="PUT" />
    <input value="REST-PUT提交"type="submit" />
<form>

@GetMapping("/user")
//@RequestMapping(value = "/user",method = RequestMethod.GET)
public String getUser(){
    return "GET-张三";
}

@PostMapping("/user")
//@RequestMapping(value = "/user",method = RequestMethod.POST)
public String saveUser(){
    return "POST-张三";
}

@PutMapping("/user")
//@RequestMapping(value = "/user",method = RequestMethod.PUT)
public String putUser(){
    return "PUT-张三";
}

@DeleteMapping("/user")
//@RequestMapping(value = "/user",method = RequestMethod.DELETE)
public String deleteUser(){
    return "DELETE-张三";
}
  • Rest原理（表单提交要使用REST的时候）
    • 表单提交会带上\_method=PUT
    • 请求过来被HiddenHttpMethodFilter拦截
      • 请求是否正常，并且是POST
        • 获取到\_method的值。
        • 兼容以下请求；PUT.DELETE.PATCH
        • 原生request（post），包装模式requesWrapper重写了getMethod方法，返回的是传入的值。
        • 过滤器链放行的时候用wrapper。以后的方法调用getMethod是调用requesWrapper的。
public class HiddenHttpMethodFilter extends OncePerRequestFilter {

	private static final List<String> ALLOWED_METHODS =
			Collections.unmodifiableList(Arrays.asList(HttpMethod.PUT.name(),
					HttpMethod.DELETE.name(), HttpMethod.PATCH.name()));

	/** Default method parameter: {@code _method}. */
	public static final String DEFAULT_METHOD_PARAM = "_method";

	private String methodParam = DEFAULT_METHOD_PARAM;


	/**
	 * Set the parameter name to look for HTTP methods.
	 * @see #DEFAULT_METHOD_PARAM
	 */
	public void setMethodParam(String methodParam) {
		Assert.hasText(methodParam, "'methodParam' must not be empty");
		this.methodParam = methodParam;
	}

	@Override
	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		HttpServletRequest requestToUse = request;

		if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {
			String paramValue = request.getParameter(this.methodParam);
			if (StringUtils.hasLength(paramValue)) {
				String method = paramValue.toUpperCase(Locale.ENGLISH);
				if (ALLOWED_METHODS.contains(method)) {
					requestToUse = new HttpMethodRequestWrapper(request, method);
				}
			}
		}

		filterChain.doFilter(requestToUse, response);
	}


	/**
	 * Simple {@link HttpServletRequest} wrapper that returns the supplied method for
	 * {@link HttpServletRequest#getMethod()}.
	 */
	private static class HttpMethodRequestWrapper extends HttpServletRequestWrapper {

		private final String method;

		public HttpMethodRequestWrapper(HttpServletRequest request, String method) {
			super(request);
			this.method = method;
		}

		@Override
		public String getMethod() {
			return this.method;
		}
	}

}
  • Rest使用客户端工具。
    • 如PostMan可直接发送put、delete等方式请求。

2.6、请求处理-【源码分析】-怎么改变默认的_method

@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {

    ...
    
    @Bean
    @ConditionalOnMissingBean(HiddenHttpMethodFilter.class)
    @ConditionalOnProperty(prefix = "spring.mvc.hiddenmethod.filter", name = "enabled", matchIfMissing = false)
    public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
        return new OrderedHiddenHttpMethodFilter();
    }
    
    ...
}

@ConditionalOnMissingBean(HiddenHttpMethodFilter.class)意味着在没有HiddenHttpMethodFilter时，才执行hiddenHttpMethodFilter()。因此，我们可以自定义filter，改变默认的\_method。例如：

@Configuration(proxyBeanMethods = false)
public class WebConfig{
    //自定义filter
    @Bean
    public HiddenHttpMethodFilter hiddenHttpMethodFilter(){
        HiddenHttpMethodFilter methodFilter = new HiddenHttpMethodFilter();
        methodFilter.setMethodParam("_m");
        return methodFilter;
    }    
}

将\_method改成_m。

<form action="/user" method="post">
    <input name="_m" type="hidden" value="DELETE"/>
    <input value="REST-DELETE 提交" type="submit"/>
</form>

2.7、请求处理-【源码分析】-请求映射原理

在这里插入图片描述

SpringMVC功能分析都从 org.springframework.web.servlet.DispatcherServlet -> doDispatch()

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    boolean multipartRequestParsed = false;

    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

    try {
        ModelAndView mv = null;
        Exception dispatchException = null;

        try {
            processedRequest = checkMultipart(request);
            multipartRequestParsed = (processedRequest != request);

            // 找到当前请求使用哪个Handler（Controller的方法）处理
            mappedHandler = getHandler(processedRequest);

            //HandlerMapping：处理器映射。/xxx->>xxxx
    ...
}

getHandler()方法如下：

@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    if (this.handlerMappings != null) {
        for (HandlerMapping mapping : this.handlerMappings) {
            HandlerExecutionChain handler = mapping.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
    }
    return null;
}

this.handlerMappings在Debug模式下展现的内容：

在这里插入图片描述

其中，保存了所有@RequestMapping 和handler的映射规则。

所有的请求映射都在HandlerMapping中：

  • SpringBoot自动配置欢迎页的 WelcomePageHandlerMapping 。访问 /能访问到index.html；

  • SpringBoot自动配置了默认 的 RequestMappingHandlerMapping

  • 请求进来，挨个尝试所有的HandlerMapping看是否有请求信息。

    • 如果有就找到这个请求对应的handler在这里插入图片描述

    • 如果没有就是下一个 HandlerMapping

  • 我们需要一些自定义的映射处理，我们也可以自己给容器中放HandlerMapping。自定义 HandlerMapping

IDEA快捷键：

  • Ctrl + Alt + U : 以UML的类图展现类有哪些继承类，派生类以及实现哪些接口。
  • Crtl + Alt + Shift + U : 同上，区别在于上条快捷键结果在新页展现，而本条快捷键结果在弹窗展现。
  • Ctrl + H : 以树形方式展现类层次结构图。

2.8、请求处理-常用参数注解使用

注解：

  • @PathVariable 路径变量
  • @RequestHeader 获取请求头
  • @RequestParam 获取请求参数（指问号后的参数，url?a=1&b=2）
  • @CookieValue 获取Cookie值
  • @RequestAttribute 获取request域属性
  • @RequestBody 获取请求体[POST]
  • @MatrixVariable 矩阵变量
  • @ModelAttribute

使用用例：

@RestController
public class ParameterTestController {


    //  car/2/owner/zhangsan
    @GetMapping("/car/{id}/owner/{username}")
    public Map<String,Object> getCar(@PathVariable("id") Integer id,
                                     @PathVariable("username") String name,
                                     @PathVariable Map<String,String> pv,
                                     @RequestHeader("User-Agent") String userAgent,
                                     @RequestHeader Map<String,String> header,
                                     @RequestParam("age") Integer age,
                                     @RequestParam("inters") List<String> inters,
                                     @RequestParam Map<String,String> params,
                                     @CookieValue("_ga") String _ga,
                                     @CookieValue("_ga") Cookie cookie){

        Map<String,Object> map = new HashMap<>();

//        map.put("id",id);
//        map.put("name",name);
//        map.put("pv",pv);
//        map.put("userAgent",userAgent);
//        map.put("headers",header);
        map.put("age",age);
        map.put("inters",inters);
        map.put("params",params);
        map.put("_ga",_ga);
        System.out.println(cookie.getName()+"===>"+cookie.getValue());
        return map;
    }


    @PostMapping("/save")
    public Map postMethod(@RequestBody String content){
        Map<String,Object> map = new HashMap<>();
        map.put("content",content);
        return map;
    }
}

2.9、请求处理-@RequestAttribute

用例：

@Controller
public class RequestController {

    @GetMapping("/goto")
    public String goToPage(HttpServletRequest request){

        request.setAttribute("msg","成功了...");
        request.setAttribute("code",200);
        return "forward:/success";  //转发到  /success请求
    }

    @GetMapping("/params")
    public String testParam(Map<String,Object> map,
                            Model model,
                            HttpServletRequest request,
                            HttpServletResponse response){
        map.put("hello","world666");
        model.addAttribute("world","hello666");
        request.setAttribute("message","HelloWorld");

        Cookie cookie = new Cookie("c1","v1");
        response.addCookie(cookie);
        return "forward:/success";
    }

    ///<-----------------主角@RequestAttribute在这个方法
    @ResponseBody
    @GetMapping("/success")
    public Map success(@RequestAttribute(value = "msg",required = false) String msg,
                       @RequestAttribute(value = "code",required = false)Integer code,
                       HttpServletRequest request){
        Object msg1 = request.getAttribute("msg");

        Map<String,Object> map = new HashMap<>();
        Object hello = request.getAttribute("hello");
        Object world = request.getAttribute("world");
        Object message = request.getAttribute("message");

        map.put("reqMethod_msg",msg1);
        map.put("annotation_msg",msg);
        map.put("hello",hello);
        map.put("world",world);
        map.put("message",message);

        return map;
    }
}

2.10、请求处理-@MatrixVariable与UrlPathHelper

  1. 语法： 请求路径：/cars/sell;low=34;brand=byd,audi,yd

  2. SpringBoot默认是禁用了矩阵变量的功能

    • 手动开启：原理。对于路径的处理。UrlPathHelper的removeSemicolonContent设置为false，让其支持矩阵变量的。

  3. 矩阵变量必须有url路径变量才能被解析

手动开启矩阵变量：

  • 实现WebMvcConfigurer接口：
@Configuration(proxyBeanMethods = false)
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void configurePathMatch(PathMatchConfigurer configurer) {

        UrlPathHelper urlPathHelper = new UrlPathHelper();
        // 不移除；后面的内容。矩阵变量功能就可以生效
        urlPathHelper.setRemoveSemicolonContent(false);
        configurer.setUrlPathHelper(urlPathHelper);
    }
}
  • 创建返回WebMvcConfigurerBean：
@Configuration(proxyBeanMethods = false)
public class WebConfig{
    @Bean
    public WebMvcConfigurer webMvcConfigurer(){
        return new WebMvcConfigurer() {
                        @Override
            public void configurePathMatch(PathMatchConfigurer configurer) {
                UrlPathHelper urlPathHelper = new UrlPathHelper();
                // 不移除；后面的内容。矩阵变量功能就可以生效
                urlPathHelper.setRemoveSemicolonContent(false);
                configurer.setUrlPathHelper(urlPathHelper);
            }
        }
    }
}

@MatrixVariable的用例

@RestController
public class ParameterTestController {

    ///cars/sell;low=34;brand=byd,audi,yd
    @GetMapping("/cars/{path}")
    public Map carsSell(@MatrixVariable("low") Integer low,
                        @MatrixVariable("brand") List<String> brand,
                        @PathVariable("path") String path){
        Map<String,Object> map = new HashMap<>();

        map.put("low",low);
        map.put("brand",brand);
        map.put("path",path);
        return map;
    }

    // /boss/1;age=20/2;age=10

    @GetMapping("/boss/{bossId}/{empId}")
    public Map boss(@MatrixVariable(value = "age",pathVar = "bossId") Integer bossAge,
                    @MatrixVariable(value = "age",pathVar = "empId") Integer empAge){
        Map<String,Object> map = new HashMap<>();

        map.put("bossAge",bossAge);
        map.put("empAge",empAge);
        return map;

    }

}

2.11、请求处理-【源码分析】-各种类型参数解析原理

这要从DispatcherServlet开始说起：

public class DispatcherServlet extends FrameworkServlet {
    
    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;
            Exception dispatchException = null;

            try {
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // Determine handler for the current request.
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
                ...
  • HandlerMapping中找到能处理请求的Handler（Controller.method()）。
  • 为当前Handler 找一个适配器 HandlerAdapter，用的最多的是RequestMappingHandlerAdapter。
  • 适配器执行目标方法并确定方法参数的每一个值。

2.11.1、HandlerAdapter

默认会加载所有HandlerAdapter

public class DispatcherServlet extends FrameworkServlet {

    /** Detect all HandlerAdapters or just expect "handlerAdapter" bean?. */
    private boolean detectAllHandlerAdapters = true;

    ...
    
    private void initHandlerAdapters(ApplicationContext context) {
        this.handlerAdapters = null;

        if (this.detectAllHandlerAdapters) {
            // Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
            Map<String, HandlerAdapter> matchingBeans =
                BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.handlerAdapters = new ArrayList<>(matchingBeans.values());
                // We keep HandlerAdapters in sorted order.
                AnnotationAwareOrderComparator.sort(this.handlerAdapters);
            }
        }
     ...

有这些HandlerAdapter：

在这里插入图片描述

  1. 支持方法上标注@RequestMapping

  2. 支持函数式编程的

  3. …

  4. …

2.11.2、执行目标方法

public class DispatcherServlet extends FrameworkServlet {
    
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        ModelAndView mv = null;
        
        ...

        // Determine handler for the current request.
        mappedHandler = getHandler(processedRequest);
        if (mappedHandler == null) {
            noHandlerFound(processedRequest, response);
            return;
        }

        // Determine handler adapter for the current request.
        HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

        ...
		//本节重点
        // Actually invoke the handler.
        mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

HandlerAdapter接口实现类RequestMappingHandlerAdapter（主要用来处理@RequestMapping）

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {

    ...
    
    //AbstractHandlerMethodAdapter类的方法，RequestMappingHandlerAdapter继承AbstractHandlerMethodAdapter
	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
        throws Exception {

        return handleInternal(request, response, (HandlerMethod) handler);
    }

	@Override
	protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
    	ModelAndView mav;
        //handleInternal的核心
        mav = invokeHandlerMethod(request, response, handlerMethod);//解释看下节
		//...
		return mav;
    }
}

2.11.3、 参数解析器

确定将要执行的目标方法的每一个参数的值是什么;

SpringMVC目标方法能写多少种参数类型。取决于参数解析器argumentResolvers。

@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
                                           HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

    ServletWebRequest webRequest = new ServletWebRequest(request, response);
    try {
        WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
        ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

        ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
        if (this.argumentResolvers != null) {//<-----关注点
            invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
        }
        
        ...

this.argumentResolvers在afterPropertiesSet()方法内初始化

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {
	
    @Nullable
    private HandlerMethodArgumentResolverComposite argumentResolvers;
    
    @Override
    public void afterPropertiesSet() {
        ...
    	if (this.argumentResolvers == null) {//初始化argumentResolvers
        	List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
            this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
        }
        ...
    }

    //初始化了一堆的实现HandlerMethodArgumentResolver接口的
	private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {
		List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>(30);

		// Annotation-based argument resolution
		resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));
		resolvers.add(new RequestParamMapMethodArgumentResolver());
		resolvers.add(new PathVariableMethodArgumentResolver());
		resolvers.add(new PathVariableMapMethodArgumentResolver());
		resolvers.add(new MatrixVariableMethodArgumentResolver());
		resolvers.add(new MatrixVariableMapMethodArgumentResolver());
		resolvers.add(new ServletModelAttributeMethodProcessor(false));
		resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
		resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters(), this.requestResponseBodyAdvice));
		resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));
		resolvers.add(new RequestHeaderMapMethodArgumentResolver());
		resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory()));
		resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));
		resolvers.add(new SessionAttributeMethodArgumentResolver());
		resolvers.add(new RequestAttributeMethodArgumentResolver());

		// Type-based argument resolution
		resolvers.add(new ServletRequestMethodArgumentResolver());
		resolvers.add(new ServletResponseMethodArgumentResolver());
		resolvers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));
		resolvers.add(new RedirectAttributesMethodArgumentResolver());
		resolvers.add(new ModelMethodProcessor());
		resolvers.add(new MapMethodProcessor());
		resolvers.add(new ErrorsMethodArgumentResolver());
		resolvers.add(new SessionStatusMethodArgumentResolver());
		resolvers.add(new UriComponentsBuilderMethodArgumentResolver());
		if (KotlinDetector.isKotlinPresent()) {
			resolvers.add(new ContinuationHandlerMethodArgumentResolver());
		}

		// Custom arguments
		if (getCustomArgumentResolvers() != null) {
			resolvers.addAll(getCustomArgumentResolvers());
		}

		// Catch-all
		resolvers.add(new PrincipalMethodArgumentResolver());
		resolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));
		resolvers.add(new ServletModelAttributeMethodProcessor(true));

		return resolvers;
	}
    
}

HandlerMethodArgumentResolverComposite类如下：（众多参数解析器argumentResolvers的包装类）。

public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {

	private final List<HandlerMethodArgumentResolver> argumentResolvers = new ArrayList<>();
    
    ...
    
	public HandlerMethodArgumentResolverComposite addResolvers(
			@Nullable HandlerMethodArgumentResolver... resolvers) {

		if (resolvers != null) {
			Collections.addAll(this.argumentResolvers, resolvers);
		}
		return this;
	}
    
    ...
}

我们看看HandlerMethodArgumentResolver的源码：

public interface HandlerMethodArgumentResolver {

    //当前解析器是否支持解析这种参数
	boolean supportsParameter(MethodParameter parameter);

	@Nullable//如果支持，就调用 resolveArgument
	Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;

}

2.11.4、 返回值处理器

ValueHandler

@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
                                           HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

    ServletWebRequest webRequest = new ServletWebRequest(request, response);
    try {
        WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
        ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

        ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
        if (this.argumentResolvers != null) {
            invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
        }
        if (this.returnValueHandlers != null) {//<---关注点
            invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
        }
     ...

this.returnValueHandlers在afterPropertiesSet()方法内初始化

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {
	
	@Nullable
	private HandlerMethodReturnValueHandlerComposite returnValueHandlers;
    
	@Override
	public void afterPropertiesSet() {

        ...
        
		if (this.returnValueHandlers == null) {
			List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
			this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
		}
	}
    
    //初始化了一堆的实现HandlerMethodReturnValueHandler接口的
    private List<HandlerMethodReturnValueHandler> getDefaultReturnValueHandlers() {
		List<HandlerMethodReturnValueHandler> handlers = new ArrayList<>(20);

		// Single-purpose return value types
		handlers.add(new ModelAndViewMethodReturnValueHandler());
		handlers.add(new ModelMethodProcessor());
		handlers.add(new ViewMethodReturnValueHandler());
		handlers.add(new ResponseBodyEmitterReturnValueHandler(getMessageConverters(),
				this.reactiveAdapterRegistry, this.taskExecutor, this.contentNegotiationManager));
		handlers.add(new StreamingResponseBodyReturnValueHandler());
		handlers.add(new HttpEntityMethodProcessor(getMessageConverters(),
				this.contentNegotiationManager, this.requestResponseBodyAdvice));
		handlers.add(new HttpHeadersReturnValueHandler());
		handlers.add(new CallableMethodReturnValueHandler());
		handlers.add(new DeferredResultMethodReturnValueHandler());
		handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));

		// Annotation-based return value types
		handlers.add(new ServletModelAttributeMethodProcessor(false));
		handlers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(),
				this.contentNegotiationManager, this.requestResponseBodyAdvice));

		// Multi-purpose return value types
		handlers.add(new ViewNameMethodReturnValueHandler());
		handlers.add(new MapMethodProcessor());

		// Custom return value types
		if (getCustomReturnValueHandlers() != null) {
			handlers.addAll(getCustomReturnValueHandlers());
		}

		// Catch-all
		if (!CollectionUtils.isEmpty(getModelAndViewResolvers())) {
			handlers.add(new ModelAndViewResolverMethodReturnValueHandler(getModelAndViewResolvers()));
		}
		else {
			handlers.add(new ServletModelAttributeMethodProcessor(true));
		}

		return handlers;
	}
}

HandlerMethodReturnValueHandlerComposite类如下：

public class HandlerMethodReturnValueHandlerComposite implements HandlerMethodReturnValueHandler {

	private final List<HandlerMethodReturnValueHandler> returnValueHandlers = new ArrayList<>();

    ...
    
	public HandlerMethodReturnValueHandlerComposite addHandlers(
			@Nullable List<? extends HandlerMethodReturnValueHandler> handlers) {

		if (handlers != null) {
			this.returnValueHandlers.addAll(handlers);
		}
		return this;
	}

}

HandlerMethodReturnValueHandler接口：

public interface HandlerMethodReturnValueHandler {

	boolean supportsReturnType(MethodParameter returnType);

	void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;

}

2.11.5、 回顾执行目标方法

public class DispatcherServlet extends FrameworkServlet {
    ...
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        ModelAndView mv = null;
		...
        mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

RequestMappingHandlerAdapter的handle()方法：

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {

    ...
    
    //AbstractHandlerMethodAdapter类的方法，RequestMappingHandlerAdapter继承AbstractHandlerMethodAdapter
	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
        throws Exception {

        return handleInternal(request, response, (HandlerMethod) handler);
    }

	@Override
	protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
    	ModelAndView mav;
        //handleInternal的核心
        mav = invokeHandlerMethod(request, response, handlerMethod);//解释看下节
		//...
		return mav;
    }
}

RequestMappingHandlerAdapter的invokeHandlerMethod()方法：

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {
    
	protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		try {
			...
            
            ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
			if (this.argumentResolvers != null) {
				invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
			}
			if (this.returnValueHandlers != null) {
				invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
			}
			...

            //关注点：执行目标方法
			invocableMethod.invokeAndHandle(webRequest, mavContainer);
			if (asyncManager.isConcurrentHandlingStarted()) {
				return null;
			}

			return getModelAndView(mavContainer, modelFactory, webRequest);
		}
		finally {
			webRequest.requestCompleted();
		}
	}

invokeAndHandle()方法如下：

public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {

	public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);

        ...
        
		try {
            //returnValue存储起来
			this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
		}
		catch (Exception ex) {
			...
		}
	}
    
    @Nullable//InvocableHandlerMethod类的，ServletInvocableHandlerMethod类继承InvocableHandlerMethod类
	public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

        获取方法的参数值
		Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);

        ...
       
		return doInvoke(args);
	}

    @Nullable
	protected Object doInvoke(Object... args) throws Exception {
		Method method = getBridgedMethod();//@RequestMapping的方法
		ReflectionUtils.makeAccessible(method);
		try {
			if (KotlinDetector.isSuspendingFunction(method)) {
				return CoroutinesUtils.invokeSuspendingFunction(method, getBean(), args);
			}
            //通过反射调用
			return method.invoke(getBean(), args);//getBean()指@RequestMapping的方法所在类的对象。
		}
		catch (IllegalArgumentException ex) {
			...
		}
		catch (InvocationTargetException ex) {
			...
		}
	}
    
}

2.11.6 、如何确定目标方法每一个参数的值

重点分析ServletInvocableHandlerMethod的getMethodArgumentValues方法

public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {
    ...

	@Nullable//InvocableHandlerMethod类的，ServletInvocableHandlerMethod类继承InvocableHandlerMethod类
	public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

        获取方法的参数值
		Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);

        ...
       
		return doInvoke(args);
	}
 
    //本节重点，获取方法的参数值
	protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		MethodParameter[] parameters = getMethodParameters();
		if (ObjectUtils.isEmpty(parameters)) {
			return EMPTY_ARGS;
		}

		Object[] args = new Object[parameters.length];
		for (int i = 0; i < parameters.length; i++) {
			MethodParameter parameter = parameters[i];
			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
			args[i] = findProvidedArgument(parameter, providedArgs);
			if (args[i] != null) {
				continue;
			}
            //查看resolvers是否有支持
			if (!this.resolvers.supportsParameter(parameter)) {
				throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
			}
			try {
                //支持的话就开始解析吧
				args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
			}
			catch (Exception ex) {
				....
			}
		}
		return args;
	}
    
}

this.resolvers的类型为HandlerMethodArgumentResolverComposite（在参数解析器章节提及）

public class HandlerMethodArgumentResolverComposite implements HandlerMethodArgumentResolver {
    
	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return getArgumentResolver(parameter) != null;
	}

	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
		if (resolver == null) {
			throw new IllegalArgumentException("Unsupported parameter type [" +
					parameter.getParameterType().getName() + "]. supportsParameter should be called first.");
		}
		return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
	}
    
    
    @Nullable
	private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) {
		HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter);
		if (result == null) {
            //挨个判断所有参数解析器那个支持解析这个参数
			for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) {
				if (resolver.supportsParameter(parameter)) {
					result = resolver;
					this.argumentResolverCache.put(parameter, result);//找到了，resolver就缓存起来，方便稍后resolveArgument()方法使用
					break;
				}
			}
		}
		return result;
	}
}

2.11.7、小结

本节描述，一个请求发送到DispatcherServlet后的具体处理流程，也就是SpringMVC的主要原理。

本节内容较多且硬核，对日后编程很有帮助，需耐心对待。

可以运行一个示例，打断点，在Debug模式下，查看程序流程。

2.12、请求处理-【源码分析】-Servlet API参数解析原理

  • WebRequest
  • ServletRequest
  • MultipartRequest
  • HttpSession
  • javax.servlet.http.PushBuilder
  • Principal
  • InputStream
  • Reader
  • HttpMethod
  • Locale
  • TimeZone
  • ZoneId

ServletRequestMethodArgumentResolver用来处理以上的参数

public class ServletRequestMethodArgumentResolver implements HandlerMethodArgumentResolver {

	@Nullable
	private static Class<?> pushBuilder;

	static {
		try {
			pushBuilder = ClassUtils.forName("javax.servlet.http.PushBuilder",
					ServletRequestMethodArgumentResolver.class.getClassLoader());
		}
		catch (ClassNotFoundException ex) {
			// Servlet 4.0 PushBuilder not found - not supported for injection
			pushBuilder = null;
		}
	}


	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		Class<?> paramType = parameter.getParameterType();
		return (WebRequest.class.isAssignableFrom(paramType) ||
				ServletRequest.class.isAssignableFrom(paramType) ||
				MultipartRequest.class.isAssignableFrom(paramType) ||
				HttpSession.class.isAssignableFrom(paramType) ||
				(pushBuilder != null && pushBuilder.isAssignableFrom(paramType)) ||
				(Principal.class.isAssignableFrom(paramType) && !parameter.hasParameterAnnotations()) ||
				InputStream.class.isAssignableFrom(paramType) ||
				Reader.class.isAssignableFrom(paramType) ||
				HttpMethod.class == paramType ||
				Locale.class == paramType ||
				TimeZone.class == paramType ||
				ZoneId.class == paramType);
	}

	@Override
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		Class<?> paramType = parameter.getParameterType();

		// WebRequest / NativeWebRequest / ServletWebRequest
		if (WebRequest.class.isAssignableFrom(paramType)) {
			if (!paramType.isInstance(webRequest)) {
				throw new IllegalStateException(
						"Current request is not of type [" + paramType.getName() + "]: " + webRequest);
			}
			return webRequest;
		}

		// ServletRequest / HttpServletRequest / MultipartRequest / MultipartHttpServletRequest
		if (ServletRequest.class.isAssignableFrom(paramType) || MultipartRequest.class.isAssignableFrom(paramType)) {
			return resolveNativeRequest(webRequest, paramType);
		}

		// HttpServletRequest required for all further argument types
		return resolveArgument(paramType, resolveNativeRequest(webRequest, HttpServletRequest.class));
	}

	private <T> T resolveNativeRequest(NativeWebRequest webRequest, Class<T> requiredType) {
		T nativeRequest = webRequest.getNativeRequest(requiredType);
		if (nativeRequest == null) {
			throw new IllegalStateException(
					"Current request is not of type [" + requiredType.getName() + "]: " + webRequest);
		}
		return nativeRequest;
	}

	@Nullable
	private Object resolveArgument(Class<?> paramType, HttpServletRequest request) throws IOException {
		if (HttpSession.class.isAssignableFrom(paramType)) {
			HttpSession session = request.getSession();
			if (session != null && !paramType.isInstance(session)) {
				throw new IllegalStateException(
						"Current session is not of type [" + paramType.getName() + "]: " + session);
			}
			return session;
		}
		else if (pushBuilder != null && pushBuilder.isAssignableFrom(paramType)) {
			return PushBuilderDelegate.resolvePushBuilder(request, paramType);
		}
		else if (InputStream.class.isAssignableFrom(paramType)) {
			InputStream inputStream = request.getInputStream();
			if (inputStream != null && !paramType.isInstance(inputStream)) {
				throw new IllegalStateException(
						"Request input stream is not of type [" + paramType.getName() + "]: " + inputStream);
			}
			return inputStream;
		}
		else if (Reader.class.isAssignableFrom(paramType)) {
			Reader reader = request.getReader();
			if (reader != null && !paramType.isInstance(reader)) {
				throw new IllegalStateException(
						"Request body reader is not of type [" + paramType.getName() + "]: " + reader);
			}
			return reader;
		}
		else if (Principal.class.isAssignableFrom(paramType)) {
			Principal userPrincipal = request.getUserPrincipal();
			if (userPrincipal != null && !paramType.isInstance(userPrincipal)) {
				throw new IllegalStateException(
						"Current user principal is not of type [" + paramType.getName() + "]: " + userPrincipal);
			}
			return userPrincipal;
		}
		else if (HttpMethod.class == paramType) {
			return HttpMethod.resolve(request.getMethod());
		}
		else if (Locale.class == paramType) {
			return RequestContextUtils.getLocale(request);
		}
		else if (TimeZone.class == paramType) {
			TimeZone timeZone = RequestContextUtils.getTimeZone(request);
			return (timeZone != null ? timeZone : TimeZone.getDefault());
		}
		else if (ZoneId.class == paramType) {
			TimeZone timeZone = RequestContextUtils.getTimeZone(request);
			return (timeZone != null ? timeZone.toZoneId() : ZoneId.systemDefault());
		}

		// Should never happen...
		throw new UnsupportedOperationException("Unknown parameter type: " + paramType.getName());
	}


	/**
	 * Inner class to avoid a hard dependency on Servlet API 4.0 at runtime.
	 */
	private static class PushBuilderDelegate {

		@Nullable
		public static Object resolvePushBuilder(HttpServletRequest request, Class<?> paramType) {
			PushBuilder pushBuilder = request.newPushBuilder();
			if (pushBuilder != null && !paramType.isInstance(pushBuilder)) {
				throw new IllegalStateException(
						"Current push builder is not of type [" + paramType.getName() + "]: " + pushBuilder);
			}
			return pushBuilder;

		}
	}
}

用例：

@Controller
public class RequestController {

    @GetMapping("/goto")
    public String goToPage(HttpServletRequest request){

        request.setAttribute("msg","成功了...");
        request.setAttribute("code",200);
        return "forward:/success";  //转发到  /success请求
    }
}

2.13、请求处理-【源码分析】-Model、Map原理

复杂参数：

  • Map

  • Model（map、model里面的数据会被放在request的请求域 request.setAttribute）

  • Errors/BindingResult

  • RedirectAttributes（ 重定向携带数据）

  • ServletResponse（response）

  • SessionStatus

  • UriComponentsBuilder

  • ServletUriComponentsBuilder

用例：

@GetMapping("/params")
public String testParam(Map<String,Object> map,
                        Model model,
                        HttpServletRequest request,
                        HttpServletResponse response){
    //下面三位都是可以给request域中放数据
    map.put("hello","world666");
    model.addAttribute("world","hello666");
    request.setAttribute("message","HelloWorld");

    Cookie cookie = new Cookie("c1","v1");
    response.addCookie(cookie);
    return "forward:/success";
}

@ResponseBody
@GetMapping("/success")
public Map success(@RequestAttribute(value = "msg",required = false) String msg,
                   @RequestAttribute(value = "code",required = false)Integer code,
                   HttpServletRequest request){
    Object msg1 = request.getAttribute("msg");

    Map<String,Object> map = new HashMap<>();
    Object hello = request.getAttribute("hello");//得出testParam方法赋予的值 world666
    Object world = request.getAttribute("world");//得出testParam方法赋予的值 hello666
    Object message = request.getAttribute("message");//得出testParam方法赋予的值 HelloWorld

    map.put("reqMethod_msg",msg1);
    map.put("annotation_msg",msg);
    map.put("hello",hello);
    map.put("world",world);
    map.put("message",message);

    return map;
}

  • Map<String,Object> map

  • Model model

  • HttpServletRequest request

上面三位都是可以给request域中放数据，用request.getAttribute()获取

接下来我们看看，Map<String,Object> map与Model model用什么参数处理器。

Map<String,Object> map参数用MapMethodProcessor处理：

public class MapMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return (Map.class.isAssignableFrom(parameter.getParameterType()) &&
				parameter.getParameterAnnotations().length == 0);
	}

	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
		return mavContainer.getModel();
	}
    
    ...
    
}

mavContainer.getModel()如下：

public class ModelAndViewContainer {

    ...

	private final ModelMap defaultModel = new BindingAwareModelMap();

	@Nullable
	private ModelMap redirectModel;

    ...

	public ModelMap getModel() {
		if (useDefaultModel()) {
			return this.defaultModel;
		}
		else {
			if (this.redirectModel == null) {
				this.redirectModel = new ModelMap();
			}
			return this.redirectModel;
		}
	}
    
    private boolean useDefaultModel() {
		return (!this.redirectModelScenario || (this.redirectModel == null && !this.ignoreDefaultModelOnRedirect));
	}
    ...
    
}

Model model用ModelMethodProcessor处理：

public class ModelMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {

	@Override
	public boolean supportsParameter(MethodParameter parameter) {
		return Model.class.isAssignableFrom(parameter.getParameterType());
	}

	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
		return mavContainer.getModel();
	}
    ...
}

return mavContainer.getModel();这跟MapMethodProcessor的一致

在这里插入图片描述

Model也是另一种意义的Map。

接下来看看Map<String,Object> map与Model model值是如何做到用request.getAttribute()获取的。

众所周知，所有的数据都放在 ModelAndView包含要去的页面地址View，还包含Model数据。

先看ModelAndView接下来是如何处理的？

public class DispatcherServlet extends FrameworkServlet {
    
    ...
    
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		...

		try {
			ModelAndView mv = null;
            
            ...

			// Actually invoke the handler.
			mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
            
            ...
            
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			catch (Throwable err) {
				// As of 4.3, we're processing Errors thrown from handler methods as well,
				// making them available for @ExceptionHandler methods and other scenarios.
				dispatchException = new NestedServletException("Handler dispatch failed", err);
			}
        	//处理分发结果
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
        ...

	}

	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {
        ...

		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			...
		}
		...
	}

	protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
		...

		View view;
		String viewName = mv.getViewName();
		if (viewName != null) {
			// We need to resolve the view name.
			view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
			if (view == null) {
				throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
						"' in servlet with name '" + getServletName() + "'");
			}
		}
		else {
			// No need to lookup: the ModelAndView object contains the actual View object.
			view = mv.getView();
			if (view == null) {
				throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
						"View object in servlet with name '" + getServletName() + "'");
			}
		}
		view.render(mv.getModelInternal(), request, response);
        
        ...
	}

}

在Debug模式下，view属为InternalResourceView类。

public class InternalResourceView extends AbstractUrlBasedView {
    
 	@Override//该方法在AbstractView，AbstractUrlBasedView继承了AbstractView
	public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
			HttpServletResponse response) throws Exception {
		
        ...
        
		Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
		prepareResponse(request, response);
        
        //看下一个方法实现
		renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
	}
    
    @Override
	protected void renderMergedOutputModel(
			Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {

		// Expose the model object as request attributes.
        // 暴露模型作为请求域属性
		exposeModelAsRequestAttributes(model, request);//<---重点

		// Expose helpers as request attributes, if any.
		exposeHelpers(request);

		// Determine the path for the request dispatcher.
		String dispatcherPath = prepareForRendering(request, response);

		// Obtain a RequestDispatcher for the target resource (typically a JSP).
		RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
		
        ...
	}
    
    //该方法在AbstractView，AbstractUrlBasedView继承了AbstractView
    protected void exposeModelAsRequestAttributes(Map<String, Object> model,
			HttpServletRequest request) throws Exception {

		model.forEach((name, value) -> {
			if (value != null) {
				request.setAttribute(name, value);
			}
			else {
				request.removeAttribute(name);
			}
		});
	}
    
}

exposeModelAsRequestAttributes方法看出，Map<String,Object> map，Model model这两种类型数据可以给request域中放数据，用request.getAttribute()获取。

2.14、请求处理-【源码分析】-自定义参数绑定原理

@RestController
public class ParameterTestController {

    /**
     * 数据绑定：页面提交的请求数据（GET、POST）都可以和对象属性进行绑定
     * @param person
     * @return
     */
    @PostMapping("/saveuser")
    public Person saveuser(Person person){
        return person;
    }
}

/**
 *     姓名： <input name="userName"/> <br/>
 *     年龄： <input name="age"/> <br/>
 *     生日： <input name="birth"/> <br/>
 *     宠物姓名：<input name="pet.name"/><br/>
 *     宠物年龄：<input name="pet.age"/>
 */
@Data
public class Person {
    
    private String userName;
    private Integer age;
    private Date birth;
    private Pet pet;
    
}

@Data
public class Pet {

    private String name;
    private String age;

}

封装过程用到ServletModelAttributeMethodProcessor

public class ServletModelAttributeMethodProcessor extends ModelAttributeMethodProcessor {
	
    @Override//本方法在ModelAttributeMethodProcessor类，
	public boolean supportsParameter(MethodParameter parameter) {
		return (parameter.hasParameterAnnotation(ModelAttribute.class) ||
				(this.annotationNotRequired && !BeanUtils.isSimpleProperty(parameter.getParameterType())));
	}

	@Override
	@Nullable//本方法在ModelAttributeMethodProcessor类，
	public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		...

		String name = ModelFactory.getNameForParameter(parameter);
		ModelAttribute ann = parameter.getParameterAnnotation(ModelAttribute.class);
		if (ann != null) {
			mavContainer.setBinding(name, ann.binding());
		}

		Object attribute = null;
		BindingResult bindingResult = null;

		if (mavContainer.containsAttribute(name)) {
			attribute = mavContainer.getModel().get(name);
		}
		else {
			// Create attribute instance
			try {
				attribute = createAttribute(name, parameter, binderFactory, webRequest);
			}
			catch (BindException ex) {
				...
			}
		}

		if (bindingResult == null) {
			// Bean property binding and validation;
			// skipped in case of binding failure on construction.
			WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
			if (binder.getTarget() != null) {
				if (!mavContainer.isBindingDisabled(name)) {
                    //web数据绑定器，将请求参数的值绑定到指定的JavaBean里面**
					bindRequestParameters(binder, webRequest);
				}
				validateIfApplicable(binder, parameter);
				if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
					throw new BindException(binder.getBindingResult());
				}
			}
			// Value type adaptation, also covering java.util.Optional
			if (!parameter.getParameterType().isInstance(attribute)) {
				attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
			}
			bindingResult = binder.getBindingResult();
		}

		// Add resolved attribute and BindingResult at the end of the model
		Map<String, Object> bindingResultModel = bindingResult.getModel();
		mavContainer.removeAttributes(bindingResultModel);
		mavContainer.addAllAttributes(bindingResultModel);

		return attribute;
	}
}

WebDataBinder 利用它里面的 Converters 将请求数据转成指定的数据类型。再次封装到JavaBean中

在过程当中，用到GenericConversionService：在设置每一个值的时候，找它里面的所有converter那个可以将这个数据类型（request带来参数的字符串）转换到指定的类型

2.15、请求处理-【源码分析】-自定义Converter原理

未来我们可以给WebDataBinder里面放自己的Converter；

下面演示将字符串“啊猫,3”转换成Pet对象。

    //1、WebMvcConfigurer定制化SpringMVC的功能
    @Bean
    public WebMvcConfigurer webMvcConfigurer(){
        return new WebMvcConfigurer() {

            @Override
            public void addFormatters(FormatterRegistry registry) {
                registry.addConverter(new Converter<String, Pet>() {

                    @Override
                    public Pet convert(String source) {
                        // 啊猫,3
                        if(!StringUtils.isEmpty(source)){
                            Pet pet = new Pet();
                            String[] split = source.split(",");
                            pet.setName(split[0]);
                            pet.setAge(Integer.parseInt(split[1]));
                            return pet;
                        }
                        return null;
                    }
                });
            }
        };
    }

2.16、响应处理-【源码分析】-ReturnValueHandler原理

在这里插入图片描述

假设给前端自动返回json数据，需要引入相关的依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<!-- web场景自动引入了json场景 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-json</artifactId>
    <version>2.3.4.RELEASE</version>
    <scope>compile</scope>
</dependency>

控制层代码如下：

@Controller
public class ResponseTestController {
    
	@ResponseBody  //利用返回值处理器里面的消息转换器进行处理
    @GetMapping(value = "/test/person")
    public Person getPerson(){
        Person person = new Person();
        person.setAge(28);
        person.setBirth(new Date());
        person.setUserName("zhangsan");
        return person;
    }

}

2.11、请求处理-【源码分析】-各种类型参数解析原理有讨论ReturnValueHandler。现在直接看看重点：

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {

    ...
    
	@Nullable
	protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		try {
			
            ...
            
            ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
                
			if (this.argumentResolvers != null) {
				invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
			}
			if (this.returnValueHandlers != null) {//<----关注点
				invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
			}

            ...

			invocableMethod.invokeAndHandle(webRequest, mavContainer);//看下块代码
			if (asyncManager.isConcurrentHandlingStarted()) {
				return null;
			}

			return getModelAndView(mavContainer, modelFactory, webRequest);
		}
		finally {
			webRequest.requestCompleted();
		}
	}

public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {
    
	public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		
        ...
        
		try {
            //看下块代码
			this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
		}
		catch (Exception ex) {
			...
		}
	}

public class HandlerMethodReturnValueHandlerComposite implements HandlerMethodReturnValueHandler {
    
    ...
    
	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

        //selectHandler()实现在下面
		HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
		if (handler == null) {
			throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
		}
        //开始处理
		handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
	}
    
   	@Nullable
	private HandlerMethodReturnValueHandler selectHandler(@Nullable Object value, MethodParameter returnType) {
		boolean isAsyncValue = isAsyncReturnValue(value, returnType);
		for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
			if (isAsyncValue && !(handler instanceof AsyncHandlerMethodReturnValueHandler)) {
				continue;
			}
			if (handler.supportsReturnType(returnType)) {
				return handler;
			}
		}
		return null;
	}

@ResponseBody 注解，即RequestResponseBodyMethodProcessor，它实现HandlerMethodReturnValueHandler接口

public class RequestResponseBodyMethodProcessor extends AbstractMessageConverterMethodProcessor {

    ...
    
	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest)
			throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

		mavContainer.setRequestHandled(true);
		ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
		ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);

        // 使用消息转换器进行写出操作，本方法下一章节介绍：
		// Try even with null return value. ResponseBodyAdvice could get involved.
		writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);
	}

}

2.17、响应处理-【源码分析】-HTTPMessageConverter原理

返回值处理器ReturnValueHandler原理：

  1. 返回值处理器判断是否支持这种类型返回值 supportsReturnType
  2. 返回值处理器调用 handleReturnValue 进行处理
  3. RequestResponseBodyMethodProcessor 可以处理返回值标了@ResponseBody 注解的。
    • 利用 MessageConverters 进行处理 将数据写为json
      1. 内容协商（浏览器默认会以请求头的方式告诉服务器他能接受什么样的内容类型）
      2. 服务器最终根据自己自身的能力，决定服务器能生产出什么样内容类型的数据，
      3. SpringMVC会挨个遍历所有容器底层的 HttpMessageConverter ，看谁能处理？
        1. 得到MappingJackson2HttpMessageConverter可以将对象写为json
        2. 利用MappingJackson2HttpMessageConverter将对象转为json再写出去。

//RequestResponseBodyMethodProcessor继承这类
public abstract class AbstractMessageConverterMethodProcessor extends AbstractMessageConverterMethodArgumentResolver
		implements HandlerMethodReturnValueHandler {

    ...
    
    //承接上一节内容
    protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
                ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
                throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

            Object body;
            Class<?> valueType;
            Type targetType;

            if (value instanceof CharSequence) {
                body = value.toString();
                valueType = String.class;
                targetType = String.class;
            }
            else {
                body = value;
                valueType = getReturnValueType(body, returnType);
                targetType = GenericTypeResolver.resolveType(getGenericType(returnType), returnType.getContainingClass());
            }

			...

            //内容协商（浏览器默认会以请求头(参数Accept)的方式告诉服务器他能接受什么样的内容类型）
            MediaType selectedMediaType = null;
            MediaType contentType = outputMessage.getHeaders().getContentType();
            boolean isContentTypePreset = contentType != null && contentType.isConcrete();
            if (isContentTypePreset) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Found 'Content-Type:" + contentType + "' in response");
                }
                selectedMediaType = contentType;
            }
            else {
                HttpServletRequest request = inputMessage.getServletRequest();
                List<MediaType> acceptableTypes = getAcceptableMediaTypes(request);
                //服务器最终根据自己自身的能力，决定服务器能生产出什么样内容类型的数据
                List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);

                if (body != null && producibleTypes.isEmpty()) {
                    throw new HttpMessageNotWritableException(
                            "No converter found for return value of type: " + valueType);
                }
                List<MediaType> mediaTypesToUse = new ArrayList<>();
                for (MediaType requestedType : acceptableTypes) {
                    for (MediaType producibleType : producibleTypes) {
                        if (requestedType.isCompatibleWith(producibleType)) {
                            mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));
                        }
                    }
                }
                if (mediaTypesToUse.isEmpty()) {
                    if (body != null) {
                        throw new HttpMediaTypeNotAcceptableException(producibleTypes);
                    }
                    if (logger.isDebugEnabled()) {
                        logger.debug("No match for " + acceptableTypes + ", supported: " + producibleTypes);
                    }
                    return;
                }

                MediaType.sortBySpecificityAndQuality(mediaTypesToUse);

                //选择一个MediaType
                for (MediaType mediaType : mediaTypesToUse) {
                    if (mediaType.isConcrete()) {
                        selectedMediaType = mediaType;
                        break;
                    }
                    else if (mediaType.isPresentIn(ALL_APPLICATION_MEDIA_TYPES)) {
                        selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
                        break;
                    }
                }

                if (logger.isDebugEnabled()) {
                    logger.debug("Using '" + selectedMediaType + "', given " +
                            acceptableTypes + " and supported " + producibleTypes);
                }
            }

        	
            if (selectedMediaType != null) {
                selectedMediaType = selectedMediaType.removeQualityValue();
                //本节主角：HttpMessageConverter
                for (HttpMessageConverter<?> converter : this.messageConverters) {
                    GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
                            (GenericHttpMessageConverter<?>) converter : null);
                    
                    //判断是否可写
                    if (genericConverter != null ?
                            ((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :
                            converter.canWrite(valueType, selectedMediaType)) {
                        body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
                                (Class<? extends HttpMessageConverter<?>>) converter.getClass(),
                                inputMessage, outputMessage);
                        if (body != null) {
                            Object theBody = body;
                            LogFormatUtils.traceDebug(logger, traceOn ->
                                    "Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");
                            addContentDispositionHeader(inputMessage, outputMessage);
							//开始写入
                            if (genericConverter != null) {
                                genericConverter.write(body, targetType, selectedMediaType, outputMessage);
                            }
                            else {
                                ((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
                            }
                        }
                        else {
                            if (logger.isDebugEnabled()) {
                                logger.debug("Nothing to write: null body");
                            }
                        }
                        return;
                    }
                }
            }
			...
        }

HTTPMessageConverter接口：

/**
 * Strategy interface for converting from and to HTTP requests and responses.
 */
public interface HttpMessageConverter<T> {

	/**
	 * Indicates whether the given class can be read by this converter.
	 */
	boolean canRead(Class<?> clazz, @Nullable MediaType mediaType);

	/**
	 * Indicates whether the given class can be written by this converter.
	 */
	boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType);

	/**
	 * Return the list of {@link MediaType} objects supported by this converter.
	 */
	List<MediaType> getSupportedMediaTypes();

	/**
	 * Read an object of the given type from the given input message, and returns it.
	 */
	T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
			throws IOException, HttpMessageNotReadableException;

	/**
	 * Write an given object to the given output message.
	 */
	void write(T t, @Nullable MediaType contentType, HttpOutputMessage outputMessage)
			throws IOException, HttpMessageNotWritableException;

}

HttpMessageConverter: 看是否支持将 此 Class类型的对象，转为MediaType类型的数据。

例子：Person对象转为JSON，或者 JSON转为Person，这将用到MappingJackson2HttpMessageConverter

在这里插入图片描述

public class MappingJackson2HttpMessageConverter extends AbstractJackson2HttpMessageConverter {
	...
}

关于MappingJackson2HttpMessageConverter的实例化请看下节。

2.17.1、 关于HttpMessageConverters的初始化

DispatcherServlet的初始化时会调用initHandlerAdapters(ApplicationContext context)

public class DispatcherServlet extends FrameworkServlet {
    
    ...
    
	private void initHandlerAdapters(ApplicationContext context) {
		this.handlerAdapters = null;

		if (this.detectAllHandlerAdapters) {
			// Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerAdapter> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerAdapters = new ArrayList<>(matchingBeans.values());
				// We keep HandlerAdapters in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerAdapters);
			}
		}
      ...

上述代码会加载ApplicationContext的所有HandlerAdapter，用来处理@RequestMapping的RequestMappingHandlerAdapter实现HandlerAdapter接口，RequestMappingHandlerAdapter也被实例化。

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {
    
    ...

    private List<HttpMessageConverter<?>> messageConverters;
    
    ...
    
	public RequestMappingHandlerAdapter() {
		this.messageConverters = new ArrayList<>(4);
		this.messageConverters.add(new ByteArrayHttpMessageConverter());
		this.messageConverters.add(new StringHttpMessageConverter());
		if (!shouldIgnoreXml) {
			try {
				this.messageConverters.add(new SourceHttpMessageConverter<>());
			}
			catch (Error err) {
				// Ignore when no TransformerFactory implementation is available
			}
		}
		this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
	}

在构造器中看到一堆HttpMessageConverter。接着，重点查看AllEncompassingFormHttpMessageConverter类：

public class AllEncompassingFormHttpMessageConverter extends FormHttpMessageConverter {

	/**
	 * Boolean flag controlled by a {@code spring.xml.ignore} system property that instructs Spring to
	 * ignore XML, i.e. to not initialize the XML-related infrastructure.
	 * <p>The default is "false".
	 */
	private static final boolean shouldIgnoreXml = SpringProperties.getFlag("spring.xml.ignore");

	private static final boolean jaxb2Present;

	private static final boolean jackson2Present;

	private static final boolean jackson2XmlPresent;

	private static final boolean jackson2SmilePresent;

	private static final boolean gsonPresent;

	private static final boolean jsonbPresent;

	private static final boolean kotlinSerializationJsonPresent;

	static {
		ClassLoader classLoader = AllEncompassingFormHttpMessageConverter.class.getClassLoader();
		jaxb2Present = ClassUtils.isPresent("javax.xml.bind.Binder", classLoader);
		jackson2Present = ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", classLoader) &&
						ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", classLoader);
		jackson2XmlPresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.xml.XmlMapper", classLoader);
		jackson2SmilePresent = ClassUtils.isPresent("com.fasterxml.jackson.dataformat.smile.SmileFactory", classLoader);
		gsonPresent = ClassUtils.isPresent("com.google.gson.Gson", classLoader);
		jsonbPresent = ClassUtils.isPresent("javax.json.bind.Jsonb", classLoader);
		kotlinSerializationJsonPresent = ClassUtils.isPresent("kotlinx.serialization.json.Json", classLoader);
	}


	public AllEncompassingFormHttpMessageConverter() {
		if (!shouldIgnoreXml) {
			try {
				addPartConverter(new SourceHttpMessageConverter<>());
			}
			catch (Error err) {
				// Ignore when no TransformerFactory implementation is available
			}

			if (jaxb2Present && !jackson2XmlPresent) {
				addPartConverter(new Jaxb2RootElementHttpMessageConverter());
			}
		}

		if (jackson2Present) {
			addPartConverter(new MappingJackson2HttpMessageConverter());//<----重点看这里
		}
		else if (gsonPresent) {
			addPartConverter(new GsonHttpMessageConverter());
		}
		else if (jsonbPresent) {
			addPartConverter(new JsonbHttpMessageConverter());
		}
		else if (kotlinSerializationJsonPresent) {
			addPartConverter(new KotlinSerializationJsonHttpMessageConverter());
		}

		if (jackson2XmlPresent && !shouldIgnoreXml) {
			addPartConverter(new MappingJackson2XmlHttpMessageConverter());
		}

		if (jackson2SmilePresent) {
			addPartConverter(new MappingJackson2SmileHttpMessageConverter());
		}
	}

}

public class FormHttpMessageConverter implements HttpMessageConverter<MultiValueMap<String, ?>> {
    
    ...
        
    private List<HttpMessageConverter<?>> partConverters = new ArrayList<>();
    
    ...
        
    public void addPartConverter(HttpMessageConverter<?> partConverter) {
		Assert.notNull(partConverter, "'partConverter' must not be null");
		this.partConverters.add(partConverter);
	}
    
    ...
}

在AllEncompassingFormHttpMessageConverter类构造器看到MappingJackson2HttpMessageConverter类的实例化，AllEncompassingFormHttpMessageConverter包含MappingJackson2HttpMessageConverter。

ReturnValueHandler是怎么与MappingJackson2HttpMessageConverter关联起来？请看下节。

2.17.2、ReturnValueHandler与MappingJackson2HttpMessageConverter关联

再次回顾RequestMappingHandlerAdapter

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {
    
    ...
    @Nullable
	private HandlerMethodReturnValueHandlerComposite returnValueHandlers;//我们关注的returnValueHandlers
    
   	
    @Override
	@Nullable//本方法在AbstractHandlerMethodAdapter
	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {

		return handleInternal(request, response, (HandlerMethod) handler);
	}
        
    @Override
	protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
		ModelAndView mav;
        ...
        mav = invokeHandlerMethod(request, response, handlerMethod);
        ...
		return mav;
	}
    
    @Nullable
	protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		try {
			WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
			ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

			ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
			if (this.argumentResolvers != null) {
				invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
			}
			if (this.returnValueHandlers != null) {//<---我们关注的returnValueHandlers
				invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
			}
            
            ...
            
			invocableMethod.invokeAndHandle(webRequest, mavContainer);
			if (asyncManager.isConcurrentHandlingStarted()) {
				return null;
			}

			return getModelAndView(mavContainer, modelFactory, webRequest);
		}
		finally {
			webRequest.requestCompleted();
		}
	}
    
   @Override
	public void afterPropertiesSet() {
		// Do this first, it may add ResponseBody advice beans
		
        ...
        
		if (this.returnValueHandlers == null) {//赋值returnValueHandlers
			List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
			this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
		}
	}
    
    private List<HandlerMethodReturnValueHandler> getDefaultReturnValueHandlers() {
		List<HandlerMethodReturnValueHandler> handlers = new ArrayList<>(20);

		...
		// Annotation-based return value types
        //这里就是 ReturnValueHandler与 MappingJackson2HttpMessageConverter关联 的关键点
		handlers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(),//<---MessageConverters也就传参传进来的
				this.contentNegotiationManager, this.requestResponseBodyAdvice));//
        ...

		return handlers;
	}
    
    //------
    
    public List<HttpMessageConverter<?>> getMessageConverters() {
		return this.messageConverters;
	}
    
    //RequestMappingHandlerAdapter构造器已初始化部分messageConverters
   	public RequestMappingHandlerAdapter() {
		this.messageConverters = new ArrayList<>(4);
		this.messageConverters.add(new ByteArrayHttpMessageConverter());
		this.messageConverters.add(new StringHttpMessageConverter());
		if (!shouldIgnoreXml) {
			try {
				this.messageConverters.add(new SourceHttpMessageConverter<>());
			}
			catch (Error err) {
				// Ignore when no TransformerFactory implementation is available
			}
		}
		this.messageConverters.add(new AllEncompassingFormHttpMessageConverter());
	}

    ...
              
}

应用中WebMvcAutoConfiguration（底层是WebMvcConfigurationSupport实现）传入更多messageConverters，其中就包含MappingJackson2HttpMessageConverter。

2.18、响应处理-【源码分析】-内容协商原理

根据客户端接收能力不同，返回不同媒体类型的数据。

引入XML依赖：

 <dependency>
     <groupId>com.fasterxml.jackson.dataformat</groupId>
     <artifactId>jackson-dataformat-xml</artifactId>
</dependency>

可用Postman软件分别测试返回json和xml：只需要改变请求头中Accept字段（application/json、application/xml）。

Http协议中规定的，Accept字段告诉服务器本客户端可以接收的数据类型。

内容协商原理：

  1. 判断当前响应头中是否已经有确定的媒体类型MediaType。
  2. 获取客户端（PostMan、浏览器）支持接收的内容类型。（获取客户端Accept请求头字段application/xml）（这一步在下一节有详细介绍）
    • contentNegotiationManager 内容协商管理器 默认使用基于请求头的策略
    • HeaderContentNegotiationStrategy 确定客户端可以接收的内容类型
  3. 遍历循环所有当前系统的 MessageConverter，看谁支持操作这个对象（Person）
  4. 找到支持操作Person的converter，把converter支持的媒体类型统计出来。
  5. 客户端需要application/xml，服务端有10种MediaType。
  6. 进行内容协商的最佳匹配媒体类型
  7. 用 支持 将对象转为 最佳匹配媒体类型 的converter。调用它进行转化 。

//RequestResponseBodyMethodProcessor继承这类
public abstract class AbstractMessageConverterMethodProcessor extends AbstractMessageConverterMethodArgumentResolver
		implements HandlerMethodReturnValueHandler {

    ...
    
    //跟上一节的代码一致
    protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
                ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
                throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

            Object body;
            Class<?> valueType;
            Type targetType;

            if (value instanceof CharSequence) {
                body = value.toString();
                valueType = String.class;
                targetType = String.class;
            }
            else {
                body = value;
                valueType = getReturnValueType(body, returnType);
                targetType = GenericTypeResolver.resolveType(getGenericType(returnType), returnType.getContainingClass());
            }

			...

            //本节重点
            //内容协商（浏览器默认会以请求头(参数Accept)的方式告诉服务器他能接受什么样的内容类型）
            MediaType selectedMediaType = null;
            MediaType contentType = outputMessage.getHeaders().getContentType();
            boolean isContentTypePreset = contentType != null && contentType.isConcrete();
            if (isContentTypePreset) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Found 'Content-Type:" + contentType + "' in response");
                }
                selectedMediaType = contentType;
            }
            else {
                HttpServletRequest request = inputMessage.getServletRequest();
                List<MediaType> acceptableTypes = getAcceptableMediaTypes(request);
                //服务器最终根据自己自身的能力，决定服务器能生产出什么样内容类型的数据
                List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);

                if (body != null && producibleTypes.isEmpty()) {
                    throw new HttpMessageNotWritableException(
                            "No converter found for return value of type: " + valueType);
                }
                List<MediaType> mediaTypesToUse = new ArrayList<>();
                for (MediaType requestedType : acceptableTypes) {
                    for (MediaType producibleType : producibleTypes) {
                        if (requestedType.isCompatibleWith(producibleType)) {
                            mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));
                        }
                    }
                }
                if (mediaTypesToUse.isEmpty()) {
                    if (body != null) {
                        throw new HttpMediaTypeNotAcceptableException(producibleTypes);
                    }
                    if (logger.isDebugEnabled()) {
                        logger.debug("No match for " + acceptableTypes + ", supported: " + producibleTypes);
                    }
                    return;
                }

                MediaType.sortBySpecificityAndQuality(mediaTypesToUse);

                //选择一个MediaType
                for (MediaType mediaType : mediaTypesToUse) {
                    if (mediaType.isConcrete()) {
                        selectedMediaType = mediaType;
                        break;
                    }
                    else if (mediaType.isPresentIn(ALL_APPLICATION_MEDIA_TYPES)) {
                        selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
                        break;
                    }
                }

                if (logger.isDebugEnabled()) {
                    logger.debug("Using '" + selectedMediaType + "', given " +
                            acceptableTypes + " and supported " + producibleTypes);
                }
            }

        	
            if (selectedMediaType != null) {
                selectedMediaType = selectedMediaType.removeQualityValue();
                //本节主角：HttpMessageConverter
                for (HttpMessageConverter<?> converter : this.messageConverters) {
                    GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
                            (GenericHttpMessageConverter<?>) converter : null);
                    
                    //判断是否可写
                    if (genericConverter != null ?
                            ((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :
                            converter.canWrite(valueType, selectedMediaType)) {
                        body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,
                                (Class<? extends HttpMessageConverter<?>>) converter.getClass(),
                                inputMessage, outputMessage);
                        if (body != null) {
                            Object theBody = body;
                            LogFormatUtils.traceDebug(logger, traceOn ->
                                    "Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");
                            addContentDispositionHeader(inputMessage, outputMessage);
							//开始写入
                            if (genericConverter != null) {
                                genericConverter.write(body, targetType, selectedMediaType, outputMessage);
                            }
                            else {
                                ((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
                            }
                        }
                        else {
                            if (logger.isDebugEnabled()) {
                                logger.debug("Nothing to write: null body");
                            }
                        }
                        return;
                    }
                }
            }
			...
        }

2.19、响应处理-【源码分析】-基于请求参数的内容协商原理

上一节内容协商原理的第二步：

获取客户端（PostMan、浏览器）支持接收的内容类型。（获取客户端Accept请求头字段application/xml）

  • contentNegotiationManager 内容协商管理器 默认使用基于请求头的策略
  • HeaderContentNegotiationStrategy 确定客户端可以接收的内容类型
//RequestResponseBodyMethodProcessor继承这类
public abstract class AbstractMessageConverterMethodProcessor extends AbstractMessageConverterMethodArgumentResolver
		implements HandlerMethodReturnValueHandler {

    ...
    
    //跟上一节的代码一致
    protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
                ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
                throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

            Object body;
            Class<?> valueType;
            Type targetType;
        
        	...
        
                    //本节重点
            //内容协商（浏览器默认会以请求头(参数Accept)的方式告诉服务器他能接受什么样的内容类型）
            MediaType selectedMediaType = null;
            MediaType contentType = outputMessage.getHeaders().getContentType();
            boolean isContentTypePreset = contentType != null && contentType.isConcrete();
            if (isContentTypePreset) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Found 'Content-Type:" + contentType + "' in response");
                }
                selectedMediaType = contentType;
            }
            else {
                HttpServletRequest request = inputMessage.getServletRequest();
                List<MediaType> acceptableTypes = getAcceptableMediaTypes(request);
                //服务器最终根据自己自身的能力，决定服务器能生产出什么样内容类型的数据
                List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);
            ...
            
	}
    
    //在AbstractMessageConverterMethodArgumentResolver类内
   	private List<MediaType> getAcceptableMediaTypes(HttpServletRequest request)
			throws HttpMediaTypeNotAcceptableException {

        //内容协商管理器 默认使用基于请求头的策略
		return this.contentNegotiationManager.resolveMediaTypes(new ServletWebRequest(request));
	}
        
}

public class ContentNegotiationManager implements ContentNegotiationStrategy, MediaTypeFileExtensionResolver {
	
    ...
    
    public ContentNegotiationManager() {
		this(new HeaderContentNegotiationStrategy());//内容协商管理器 默认使用基于请求头的策略
	}
    
    @Override
	public List<MediaType> resolveMediaTypes(NativeWebRequest request) throws HttpMediaTypeNotAcceptableException {
		for (ContentNegotiationStrategy strategy : this.strategies) {
			List<MediaType> mediaTypes = strategy.resolveMediaTypes(request);
			if (mediaTypes.equals(MEDIA_TYPE_ALL_LIST)) {
				continue;
			}
			return mediaTypes;
		}
		return MEDIA_TYPE_ALL_LIST;
	}
    ...
    
}

//基于请求头的策略
public class HeaderContentNegotiationStrategy implements ContentNegotiationStrategy {

	/**
	 * {@inheritDoc}
	 * @throws HttpMediaTypeNotAcceptableException if the 'Accept' header cannot be parsed
	 */
	@Override
	public List<MediaType> resolveMediaTypes(NativeWebRequest request)
			throws HttpMediaTypeNotAcceptableException {

		String[] headerValueArray = request.getHeaderValues(HttpHeaders.ACCEPT);
		if (headerValueArray == null) {
			return MEDIA_TYPE_ALL_LIST;
		}

		List<String> headerValues = Arrays.asList(headerValueArray);
		try {
			List<MediaType> mediaTypes = MediaType.parseMediaTypes(headerValues);
			MediaType.sortBySpecificityAndQuality(mediaTypes);
			return !CollectionUtils.isEmpty(mediaTypes) ? mediaTypes : MEDIA_TYPE_ALL_LIST;
		}
		catch (InvalidMediaTypeException ex) {
			throw new HttpMediaTypeNotAcceptableException(
					"Could not parse 'Accept' header " + headerValues + ": " + ex.getMessage());
		}
	}

}

2.19.1、 开启浏览器参数方式内容协商功能

为了方便内容协商，开启基于请求参数的内容协商功能。

spring:
  mvc:
    contentnegotiation:
      favor-parameter: true  #开启请求参数内容协商模式

内容协商管理器，就会多了一个ParameterContentNegotiationStrategy（由Spring容器注入）

public class ParameterContentNegotiationStrategy extends AbstractMappingContentNegotiationStrategy {

	private String parameterName = "format";//


	/**
	 * Create an instance with the given map of file extensions and media types.
	 */
	public ParameterContentNegotiationStrategy(Map<String, MediaType> mediaTypes) {
		super(mediaTypes);
	}


	/**
	 * Set the name of the parameter to use to determine requested media types.
	 * <p>By default this is set to {@code "format"}.
	 */
	public void setParameterName(String parameterName) {
		Assert.notNull(parameterName, "'parameterName' is required");
		this.parameterName = parameterName;
	}

	public String getParameterName() {
		return this.parameterName;
	}


	@Override
	@Nullable
	protected String getMediaTypeKey(NativeWebRequest request) {
		return request.getParameter(getParameterName());
	}
    
    //---以下方法在AbstractMappingContentNegotiationStrategy类
    
    @Override
	public List<MediaType> resolveMediaTypes(NativeWebRequest webRequest)
			throws HttpMediaTypeNotAcceptableException {

		return resolveMediaTypeKey(webRequest, getMediaTypeKey(webRequest));
	}

	/**
	 * An alternative to {@link #resolveMediaTypes(NativeWebRequest)} that accepts
	 * an already extracted key.
	 * @since 3.2.16
	 */
	public List<MediaType> resolveMediaTypeKey(NativeWebRequest webRequest, @Nullable String key)
			throws HttpMediaTypeNotAcceptableException {

		if (StringUtils.hasText(key)) {
			MediaType mediaType = lookupMediaType(key);
			if (mediaType != null) {
				handleMatch(key, mediaType);
				return Collections.singletonList(mediaType);
			}
			mediaType = handleNoMatch(webRequest, key);
			if (mediaType != null) {
				addMapping(key, mediaType);
				return Collections.singletonList(mediaType);
			}
		}
		return MEDIA_TYPE_ALL_LIST;
	}
    

}

然后，浏览器地址输入带format参数的URL：

http://localhost:8080/test/person?format=json
或
http://localhost:8080/test/person?format=xml

这样，后端会根据参数format的值，返回对应json或xml格式的数据。

2.20、响应处理-【源码分析】-自定义MessageConverter

实现多协议数据兼容。json、xml、x-guigu（这个是自创的）

  1. @ResponseBody 响应数据出去 调用 RequestResponseBodyMethodProcessor 处理

  2. Processor 处理方法返回值。通过 MessageConverter处理

  3. 所有 MessageConverter 合起来可以支持各种媒体类型数据的操作（读、写）

  4. 内容协商找到最终的 messageConverter

SpringMVC的什么功能，一个入口给容器中添加一个 WebMvcConfigurer

@Configuration(proxyBeanMethods = false)
public class WebConfig {
    @Bean
    public WebMvcConfigurer webMvcConfigurer(){
        return new WebMvcConfigurer() {

            @Override
            public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
                converters.add(new GuiguMessageConverter());
            }
        }
    }
}


/**
 * 自定义的Converter
 */
public class GuiguMessageConverter implements HttpMessageConverter<Person> {

    @Override
    public boolean canRead(Class<?> clazz, MediaType mediaType) {
        return false;
    }

    @Override
    public boolean canWrite(Class<?> clazz, MediaType mediaType) {
        return clazz.isAssignableFrom(Person.class);
    }

    /**
     * 服务器要统计所有MessageConverter都能写出哪些内容类型
     *
     * application/x-guigu
     * @return
     */
    @Override
    public List<MediaType> getSupportedMediaTypes() {
        return MediaType.parseMediaTypes("application/x-guigu");
    }

    @Override
    public Person read(Class<? extends Person> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
        return null;
    }

    @Override
    public void write(Person person, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
        //自定义协议数据的写出
        String data = person.getUserName()+";"+person.getAge()+";"+person.getBirth();


        //写出去
        OutputStream body = outputMessage.getBody();
        body.write(data.getBytes());
    }
}

import java.util.Date;

@Controller
public class ResponseTestController {

    /**
     * 1、浏览器发请求直接返回 xml    [application/xml]        jacksonXmlConverter
     * 2、如果是ajax请求 返回 json   [application/json]      jacksonJsonConverter
     * 3、如果硅谷app发请求，返回自定义协议数据  [appliaction/x-guigu]   xxxxConverter
     *          属性值1;属性值2;
     *
     * 步骤：
     * 1、添加自定义的MessageConverter进系统底层
     * 2、系统底层就会统计出所有MessageConverter能操作哪些类型
     * 3、客户端内容协商 [guigu--->guigu]
     *
     * 作业：如何以参数的方式进行内容协商
     * @return
     */
    @ResponseBody  //利用返回值处理器里面的消息转换器进行处理
    @GetMapping(value = "/test/person")
    public Person getPerson(){
        Person person = new Person();
        person.setAge(28);
        person.setBirth(new Date());
        person.setUserName("zhangsan");
        return person;
    }

}

用Postman发送/test/person（请求头Accept:application/x-guigu)，将返回自定义协议数据的写出。

2.21、响应处理-【源码分析】-浏览器与PostMan内容协商完全适配

假设你想基于自定义请求参数的自定义内容协商功能。

换句话，在地址栏输入http://localhost:8080/test/person?format=gg返回数据，跟http://localhost:8080/test/person且请求头参数Accept:application/x-guigu的返回自定义协议数据的一致。

@Configuration(proxyBeanMethods = false)
public class WebConfig /*implements WebMvcConfigurer*/ {

    //1、WebMvcConfigurer定制化SpringMVC的功能
    @Bean
    public WebMvcConfigurer webMvcConfigurer(){
        return new WebMvcConfigurer() {

            /**
             * 自定义内容协商策略
             * @param configurer
             */
            @Override
            public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
                //Map<String, MediaType> mediaTypes
                Map<String, MediaType> mediaTypes = new HashMap<>();
                mediaTypes.put("json",MediaType.APPLICATION_JSON);
                mediaTypes.put("xml",MediaType.APPLICATION_XML);
                //自定义媒体类型
                mediaTypes.put("gg",MediaType.parseMediaType("application/x-guigu"));
                //指定支持解析哪些参数对应的哪些媒体类型
                ParameterContentNegotiationStrategy parameterStrategy = new ParameterContentNegotiationStrategy(mediaTypes);
//                parameterStrategy.setParameterName("ff");

                //还需添加请求头处理策略，否则accept:application/json、application/xml则会失效
                HeaderContentNegotiationStrategy headeStrategy = new HeaderContentNegotiationStrategy();

                configurer.strategies(Arrays.asList(parameterStrategy, headeStrategy));
            }
        }
    }
    
    ...
    
}

日后开发要注意，有可能我们添加的自定义的功能会覆盖默认很多功能，导致一些默认的功能失效。

3、web之视图解析

3.1、Thymeleaf初体验

Thymeleaf is a modern server-side Java template engine for both web and standalone environments.

Thymeleaf’s main goal is to bring elegant natural templates to your development workflow — HTML that can be correctly displayed in browsers and also work as static prototypes, allowing for stronger collaboration in development teams.

With modules for Spring Framework, a host of integrations with your favourite tools, and the ability to plug in your own functionality, Thymeleaf is ideal for modern-day HTML5 JVM web development — although there is much more it can do.——Link

Thymeleaf官方文档

3.1.1、 thymeleaf使用

引入Starter

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

自动配置好了thymeleaf

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(ThymeleafProperties.class)
@ConditionalOnClass({ TemplateMode.class, SpringTemplateEngine.class })
@AutoConfigureAfter({ WebMvcAutoConfiguration.class, WebFluxAutoConfiguration.class })
public class ThymeleafAutoConfiguration {
    ...
}

自动配好的策略

  1. 所有thymeleaf的配置值都在 ThymeleafProperties

  2. 配置好了 SpringTemplateEngine

  3. 配好了 ThymeleafViewResolver

  4. 我们只需要直接开发页面

public static final String DEFAULT_PREFIX = "classpath:/templates/";//模板放置处
public static final String DEFAULT_SUFFIX = ".html";//文件的后缀名

编写一个控制层：

@Controller
public class ViewTestController {
    @GetMapping("/hello")
    public String hello(Model model){
        //model中的数据会被放在请求域中 request.setAttribute("a",aa)
        model.addAttribute("msg","一定要大力发展工业文化");
        model.addAttribute("link","http://www.baidu.com");
        return "success";
    }
}

/templates/success.html：

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1 th:text="${msg}">nice</h1>
<h2>
    <a href="www.baidu.com" th:href="${link}">去百度</a>  <br/>
    <a href="www.google.com" th:href="@{/link}">去百度</a>
</h2>
</body>
</html>

server:
  servlet:
    context-path: /app #设置应用名

这个设置后，URL要插入/app, 如http://localhost:8080/app/hello.html。

3.1.2、 基本语法

表达式

表达式名字语法用途
变量取值${…}获取请求域、session域、对象等值
选择变量*{…}获取上下文对象值
消息#{…}获取国际化等值
链接@{…}生成链接
片段表达式~{…}jsp:include 作用，引入公共页面片段

字面量

  • 文本值: ‘one text’ , ‘Another one!’ ,…
  • 数字: 0 , 34 , 3.0 , 12.3 ,…
  • 布尔值: true , false
  • 空值: null
  • 变量： one，two，… 变量不能有空格

文本操作

  • 字符串拼接: +
  • 变量替换: |The name is ${name}|

数学运算

  • 运算符: + , - , * , / , %

布尔运算

  • 运算符: and , or
  • 一元运算: ! , not

比较运算

  • 比较: > , < , >= , <= ( gt , lt , ge , le )
  • 等式: == , != ( eq , ne )

条件运算

  • If-then: (if) ? (then)
  • If-then-else: (if) ? (then) : (else)
  • Default: (value) ?: (defaultvalue)

特殊操作

  • 无操作： _

3.1.3、 设置属性值-th:attr

  • 设置单个值
<form action="subscribe.html" th:attr="action=@{/subscribe}">
  <fieldset>
    <input type="text" name="email" />
    <input type="submit" value="Subscribe!" th:attr="value=#{subscribe.submit}"/>
  </fieldset>
</form>
  • 设置多个值
<img src="../../images/gtvglogo.png"  
     th:attr="src=@{/images/gtvglogo.png},title=#{logo},alt=#{logo}" />

官方文档 - 5 Setting Attribute Values

3.1.4、 迭代

<tr th:each="prod : ${prods}">
    <td th:text="${prod.name}">Onions</td>
    <td th:text="${prod.price}">2.41</td>
    <td th:text="${prod.inStock}? #{true} : #{false}">yes</td>
</tr>

<tr th:each="prod,iterStat : ${prods}" th:class="${iterStat.odd}? 'odd'">
    <td th:text="${prod.name}">Onions</td>
    <td th:text="${prod.price}">2.41</td>
    <td th:text="${prod.inStock}? #{true} : #{false}">yes</td>
</tr>

3.1.5、 条件运算

<a href="comments.html"
	th:href="@{/product/comments(prodId=${prod.id})}"
	th:if="${not #lists.isEmpty(prod.comments)}">view</a>

<div th:switch="${user.role}">
      <p th:case="'admin'">User is an administrator</p>
      <p th:case="#{roles.manager}">User is a manager</p>
      <p th:case="*">User is some other thing</p>
</div>

3.1.6、属性优先级

OrderFeatureAttributes
1Fragment inclusionth:insert th:replace
2Fragment iterationth:each
3Conditional evaluationth:if th:unless th:switch th:case
4Local variable definitionth:object th:with
5General attribute modificationth:attr th:attrprepend th:attrappend
6Specific attribute modificationth:value th:href th:src ...
7Text (tag body modification)th:text th:utext
8Fragment specificationth:fragment
9Fragment removalth:remove

官方文档 - 10 Attribute Precedence

3.2、web实验-后台管理系统基本功能

3.2.1、 项目创建

使用IDEA的Spring Initializr。

  • thymeleaf、
  • web-starter、
  • devtools、
  • lombok

3.2.2、 登陆页面

  • /static 放置 css，js等静态资源

  • /templates/login.html 登录页

<html lang="en" xmlns:th="http://www.thymeleaf.org"><!-- 要加这玩意thymeleaf才能用 -->

<form class="form-signin" action="index.html" method="post" th:action="@{/login}">

    ...
    
    <!-- 消息提醒 -->
    <label style="color: red" th:text="${msg}"></label>
    
    <input type="text" name="userName" class="form-control" placeholder="User ID" autofocus>
    <input type="password" name="password" class="form-control" placeholder="Password">
    
    <button class="btn btn-lg btn-login btn-block" type="submit">
        <i class="fa fa-check"></i>
    </button>
    
    ...
    
</form>
  • /templates/main.html 主页

thymeleaf内联写法：

<p>Hello, [[${session.user.name}]]!</p>

3.2.3 、登录控制层

@Controller
public class IndexController {
    /**
     * 来登录页
     * @return
     */
    @GetMapping(value = {"/","/login"})
    public String loginPage(){

        return "login";
    }

    @PostMapping("/login")
    public String main(User user, HttpSession session, Model model){ //RedirectAttributes

        if(StringUtils.hasLength(user.getUserName()) && "123456".equals(user.getPassword())){
            //把登陆成功的用户保存起来
            session.setAttribute("loginUser",user);
            //登录成功重定向到main.html;  重定向防止表单重复提交
            return "redirect:/main.html";
        }else {
            model.addAttribute("msg","账号密码错误");
            //回到登录页面
            return "login";
        }
    }
    
     /**
     * 去main页面
     * @return
     */
    @GetMapping("/main.html")
    public String mainPage(HttpSession session, Model model){
        
        //最好用拦截器,过滤器
        Object loginUser = session.getAttribute("loginUser");
        if(loginUser != null){
        	return "main";
        }else {
            //session过期，没有登陆过
        	//回到登录页面
	        model.addAttribute("msg","请重新登录");
    	    return "login";
        }
    }
    
}

3.2.4、 模型

@AllArgsConstructor
@NoArgsConstructor
@Data
public class User {
    private String userName;
    private String password;
}

3.2.5、抽取公共页面

官方文档 - Template Layout

  • 公共页面/templates/common.html
<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org"><!--注意要添加xmlns:th才能添加thymeleaf的标签-->
<head th:fragment="commonheader">
    <!--common-->
    <link href="css/style.css" th:href="@{/css/style.css}" rel="stylesheet">
    <link href="css/style-responsive.css" th:href="@{/css/style-responsive.css}" rel="stylesheet">
    ...
</head>
<body>
<!-- left side start-->
<div id="leftmenu" class="left-side sticky-left-side">
	...

    <div class="left-side-inner">
		...

        <!--sidebar nav start-->
        <ul class="nav nav-pills nav-stacked custom-nav">
            <li><a th:href="@{/main.html}"><i class="fa fa-home"></i> <span>Dashboard</span></a></li>
            ...
            <li class="menu-list nav-active"><a href="#"><i class="fa fa-th-list"></i> <span>Data Tables</span></a>
                <ul class="sub-menu-list">
                    <li><a th:href="@{/basic_table}"> Basic Table</a></li>
                    <li><a th:href="@{/dynamic_table}"> Advanced Table</a></li>
                    <li><a th:href="@{/responsive_table}"> Responsive Table</a></li>
                    <li><a th:href="@{/editable_table}"> Edit Table</a></li>
                </ul>
            </li>
            ...
        </ul>
        <!--sidebar nav end-->
    </div>
</div>
<!-- left side end-->


<!-- header section start-->
<div th:fragment="headermenu" class="header-section">

    <!--toggle button start-->
    <a class="toggle-btn"><i class="fa fa-bars"></i></a>
    <!--toggle button end-->
	...

</div>
<!-- header section end-->

<div id="commonscript">
    <!-- Placed js at the end of the document so the pages load faster -->
    <script th:src="@{/js/jquery-1.10.2.min.js}"></script>
    <script th:src="@{/js/jquery-ui-1.9.2.custom.min.js}"></script>
    <script th:src="@{/js/jquery-migrate-1.2.1.min.js}"></script>
    <script th:src="@{/js/bootstrap.min.js}"></script>
    <script th:src="@{/js/modernizr.min.js}"></script>
    <script th:src="@{/js/jquery.nicescroll.js}"></script>
    <!--common scripts for all pages-->
    <script th:src="@{/js/scripts.js}"></script>
</div>
</body>
</html>
  • /templates/table/basic_table.html
<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
  <meta name="description" content="">
  <meta name="author" content="ThemeBucket">
  <link rel="shortcut icon" href="#" type="image/png">

  <title>Basic Table</title>
    <div th:include="common :: commonheader"> </div><!--将common.html的代码段 插进来-->
</head>

<body class="sticky-header">

<section>
<div th:replace="common :: #leftmenu"></div>
    
    <!-- main content start-->
    <div class="main-content" >

        <div th:replace="common :: headermenu"></div>
        ...
    </div>
    <!-- main content end-->
</section>

<!-- Placed js at the end of the document so the pages load faster -->
<div th:replace="common :: #commonscript"></div>


</body>
</html>

Difference between th:insert and th:replace (and th:include)

3.2.6、遍历数据与页面bug修改

控制层代码：

@GetMapping("/dynamic_table")
public String dynamic_table(Model model){
    //表格内容的遍历
    List<User> users = Arrays.asList(new User("zhangsan", "123456"),
                                     new User("lisi", "123444"),
                                     new User("haha", "aaaaa"),
                                     new User("hehe ", "aaddd"));
    model.addAttribute("users",users);

    return "table/dynamic_table";
}

页面代码：

<table class="display table table-bordered" id="hidden-table-info">
    <thead>
        <tr>
            <th>#</th>
            <th>用户名</th>
            <th>密码</th>
        </tr>
    </thead>
    <tbody>
        <tr class="gradeX" th:each="user,stats:${users}">
            <td th:text="${stats.count}">Trident</td>
            <td th:text="${user.userName}">Internet</td>
            <td >[[${user.password}]]</td>
        </tr>
    </tbody>
</table>

3.2.7、视图解析-【源码分析】-视图解析器与视图

视图解析原理流程：

  1. 目标方法处理的过程中（阅读DispatcherServlet源码），所有数据都会被放在 ModelAndViewContainer 里面，其中包括数据和视图地址。

  2. 方法的参数是一个自定义类型对象（从请求参数中确定的），把他重新放在 ModelAndViewContainer 。

  3. 任何目标方法执行完成以后都会返回ModelAndView（数据和视图地址）。

  4. processDispatchResult()处理派发结果（页面改如何响应）

    • render(mv, request, response); 进行页面渲染逻辑

      • 根据方法的String返回值得到 View 对象【定义了页面的渲染逻辑】
      1. 所有的视图解析器尝试是否能根据当前返回值得到View对象
      2. 得到了 redirect:/main.html --> Thymeleaf new RedirectView()。
      3. ContentNegotiationViewResolver 里面包含了下面所有的视图解析器，内部还是利用下面所有视图解析器得到视图对象。
      4. view.render(mv.getModelInternal(), request, response); 视图对象调用自定义的render进行页面渲染工作。
      • RedirectView 如何渲染【重定向到一个页面】
      • 获取目标url地址
      • response.sendRedirect(encodedURL);

视图解析：
- 返回值以 forward: 开始： new InternalResourceView(forwardUrl); --> 转发request.getRequestDispatcher(path).forward(request, response);
- 返回值以 redirect: 开始： new RedirectView() --> render就是重定向
- 返回值是普通字符串：new ThymeleafView()—>

阅读源码：最好自己在IDE，打断点，且Debug模式运行实例，这样比较没那么沉闷。

3.2.8、拦截器-登录检查与静态资源放行

  1. 编写一个拦截器实现HandlerInterceptor接口
  2. 拦截器注册到容器中（实现WebMvcConfigurer的addInterceptors()）
  3. 指定拦截规则（注意，如果是拦截所有，静态资源也会被拦截】

编写一个实现HandlerInterceptor接口的拦截器：

@Slf4j
public class LoginInterceptor implements HandlerInterceptor {

    /**
     * 目标方法执行之前
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

        String requestURI = request.getRequestURI();
        log.info("preHandle拦截的请求路径是{}",requestURI);

        //登录检查逻辑
        HttpSession session = request.getSession();

        Object loginUser = session.getAttribute("loginUser");

        if(loginUser != null){
            //放行
            return true;
        }

        //拦截住。未登录。跳转到登录页
        request.setAttribute("msg","请先登录");
//        re.sendRedirect("/");
        request.getRequestDispatcher("/").forward(request,response);
        return false;
    }

    /**
     * 目标方法执行完成以后
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        log.info("postHandle执行{}",modelAndView);
    }

    /**
     * 页面渲染以后
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        log.info("afterCompletion执行异常{}",ex);
    }
}

拦截器注册到容器中 && 指定拦截规则：

@Configuration
public class AdminWebConfig implements WebMvcConfigurer{
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginInterceptor())//拦截器注册到容器中
                .addPathPatterns("/**")  //所有请求都被拦截包括静态资源
                .excludePathPatterns("/","/login","/css/**","/fonts/**","/images/**",
                        "/js/**","/aa/**"); //放行的请求
}

3.2.9、拦截器-【源码分析】-拦截器的执行时机和原理

  1. 根据当前请求，找到HandlerExecutionChain（可以处理请求的handler以及handler的所有 拦截器）
  2. 先来顺序执行 所有拦截器的 preHandle()方法。
    • 如果当前拦截器preHandle()返回为true。则执行下一个拦截器的preHandle()
    • 如果当前拦截器返回为false。直接倒序执行所有已经执行了的拦截器的 afterCompletion();。
  3. 如果任何一个拦截器返回false，直接跳出不执行目标方法。
  4. 所有拦截器都返回true，才执行目标方法。
  5. 倒序执行所有拦截器的postHandle()方法。
  6. 前面的步骤有任何异常都会直接倒序触发 afterCompletion()。
  7. 页面成功渲染完成以后，也会倒序触发 afterCompletion()。

在这里插入图片描述

DispatcherServlet中涉及到HandlerInterceptor的地方：

public class DispatcherServlet extends FrameworkServlet {
    
    ...
    
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

            	...
            
                //该方法内调用HandlerInterceptor的preHandle()
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

            	...
                //该方法内调用HandlerInterceptor的postHandle()
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}			
        	processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
            //该方法内调用HandlerInterceptor接口的afterCompletion方法
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
            //该方法内调用HandlerInterceptor接口的afterCompletion方法
			triggerAfterCompletion(processedRequest, response, mappedHandler,
					new NestedServletException("Handler processing failed", err));
		}
		finally {
			...
		}
	}

	private void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, Exception ex) throws Exception {

		if (mappedHandler != null) {
            //该方法内调用HandlerInterceptor接口的afterCompletion方法
			mappedHandler.triggerAfterCompletion(request, response, ex);
		}
		throw ex;
	}

	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

        ...

		if (mappedHandler != null) {
            //该方法内调用HandlerInterceptor接口的afterCompletion方法
			// Exception (if any) is already handled..
			mappedHandler.triggerAfterCompletion(request, response, null);
		}
	}


}

public class HandlerExecutionChain {
    
    ...
    
	boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		for (int i = 0; i < this.interceptorList.size(); i++) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
            //HandlerInterceptor的preHandle方法
			if (!interceptor.preHandle(request, response, this.handler)) {
                
				triggerAfterCompletion(request, response, null);
				return false;
			}
			this.interceptorIndex = i;
		}
		return true;
	}
    
   	void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
			throws Exception {

		for (int i = this.interceptorList.size() - 1; i >= 0; i--) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
            
            //HandlerInterceptor接口的postHandle方法
			interceptor.postHandle(request, response, this.handler, mv);
		}
	}
    
    void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) {
		for (int i = this.interceptorIndex; i >= 0; i--) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			try {
                //HandlerInterceptor接口的afterCompletion方法
				interceptor.afterCompletion(request, response, this.handler, ex);
			}
			catch (Throwable ex2) {
				logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
			}
		}
	}
    
    
}

3.2.10、文件上传-单文件与多文件上传的使用

  • 页面代码/static/form/form_layouts.html
<form role="form" th:action="@{/upload}" method="post" enctype="multipart/form-data">
    <div class="form-group">
        <label for="exampleInputEmail1">邮箱</label>
        <input type="email" name="email" class="form-control" id="exampleInputEmail1" placeholder="Enter email">
    </div>
    
    <div class="form-group">
        <label for="exampleInputPassword1">名字</label>
        <input type="text" name="username" class="form-control" id="exampleInputPassword1" placeholder="Password">
    </div>
    
    <div class="form-group">
        <label for="exampleInputFile">头像</label>
        <input type="file" name="headerImg" id="exampleInputFile">
    </div>
    
    <div class="form-group">
        <label for="exampleInputFile">生活照</label>
        <input type="file" name="photos" multiple>
    </div>
    
    <div class="checkbox">
        <label>
            <input type="checkbox"> Check me out
        </label>
    </div>
    <button type="submit" class="btn btn-primary">提交</button>
</form>
  • 控制层代码
@Slf4j
@Controller
public class FormTestController {

    @GetMapping("/form_layouts")
    public String form_layouts(){
        return "form/form_layouts";
    }

    @PostMapping("/upload")
    public String upload(@RequestParam("email") String email,
                         @RequestParam("username") String username,
                         @RequestPart("headerImg") MultipartFile headerImg,
                         @RequestPart("photos") MultipartFile[] photos) throws IOException {

        log.info("上传的信息：email={}，username={}，headerImg={}，photos={}",
                 email,username,headerImg.getSize(),photos.length);

        if(!headerImg.isEmpty()){
            //保存到文件服务器，OSS服务器
            String originalFilename = headerImg.getOriginalFilename();
            headerImg.transferTo(new File("H:\\cache\\"+originalFilename));
        }

        if(photos.length > 0){
            for (MultipartFile photo : photos) {
                if(!photo.isEmpty()){
                    String originalFilename = photo.getOriginalFilename();
                    photo.transferTo(new File("H:\\cache\\"+originalFilename));
                }
            }
        }


        return "main";
    }
}

文件上传相关的配置类：

  • org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration
  • org.springframework.boot.autoconfigure.web.servlet.MultipartProperties

文件大小相关配置项：

spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=100MB

3.2.11、文件上传-【源码流程】文件上传参数解析器

文件上传相关的自动配置类MultipartAutoConfiguration有创建文件上传参数解析器StandardServletMultipartResolver。

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ Servlet.class, StandardServletMultipartResolver.class, MultipartConfigElement.class })
@ConditionalOnProperty(prefix = "spring.servlet.multipart", name = "enabled", matchIfMissing = true)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(MultipartProperties.class)
public class MultipartAutoConfiguration {

	private final MultipartProperties multipartProperties;

	public MultipartAutoConfiguration(MultipartProperties multipartProperties) {
		this.multipartProperties = multipartProperties;
	}

	@Bean
	@ConditionalOnMissingBean({ MultipartConfigElement.class, CommonsMultipartResolver.class })
	public MultipartConfigElement multipartConfigElement() {
		return this.multipartProperties.createMultipartConfig();
	}

	@Bean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
	@ConditionalOnMissingBean(MultipartResolver.class)
	public StandardServletMultipartResolver multipartResolver() {
        //配置好文件上传解析器
		StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();
		multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
		return multipartResolver;
	}

}

//文件上传解析器
public class StandardServletMultipartResolver implements MultipartResolver {

	private boolean resolveLazily = false;

	public void setResolveLazily(boolean resolveLazily) {
		this.resolveLazily = resolveLazily;
	}


	@Override
	public boolean isMultipart(HttpServletRequest request) {
		return StringUtils.startsWithIgnoreCase(request.getContentType(), "multipart/");
	}

	@Override
	public MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException {
		return new StandardMultipartHttpServletRequest(request, this.resolveLazily);
	}

	@Override
	public void cleanupMultipart(MultipartHttpServletRequest request) {
		if (!(request instanceof AbstractMultipartHttpServletRequest) ||
				((AbstractMultipartHttpServletRequest) request).isResolved()) {
			// To be on the safe side: explicitly delete the parts,
			// but only actual file parts (for Resin compatibility)
			try {
				for (Part part : request.getParts()) {
					if (request.getFile(part.getName()) != null) {
						part.delete();
					}
				}
			}
			catch (Throwable ex) {
				LogFactory.getLog(getClass()).warn("Failed to perform cleanup of multipart items", ex);
			}
		}
	}

}

public class DispatcherServlet extends FrameworkServlet {
    
    @Nullable
	private MultipartResolver multipartResolver;
    
	private void initMultipartResolver(ApplicationContext context) {
		...
        
        //这个就是配置类配置的StandardServletMultipartResolver文件上传解析器
		this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
		...
	}
    
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;//最后finally的回收flag
		...
		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {
                //做预处理,如果有上传文件 就new StandardMultipartHttpServletRequest包装类
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);
				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				
                ...

				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				...

				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
                
            }
            ....
            
		finally {

            ...
            
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
		}
	}

	protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
		if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
            ...
			return this.multipartResolver.resolveMultipart(request);
            ...
		}
    }

	protected void cleanupMultipart(HttpServletRequest request) {
		if (this.multipartResolver != null) {
			MultipartHttpServletRequest multipartRequest =
					WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
			if (multipartRequest != null) {
				this.multipartResolver.cleanupMultipart(multipartRequest);
			}
		}
	}
}

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());跳到以下的类

public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
		implements BeanFactoryAware, InitializingBean {
	@Override
	protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
		ModelAndView mav;
		...
		mav = invokeHandlerMethod(request, response, handlerMethod);
        ...
		return mav;
	}
    
    @Nullable
	protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		try {
			WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
			ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

			ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
			if (this.argumentResolvers != null) {//关注点
				invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
			}
			...
			invocableMethod.invokeAndHandle(webRequest, mavContainer);
			...

			return getModelAndView(mavContainer, modelFactory, webRequest);
		}
		finally {
			webRequest.requestCompleted();
		}
	}
    
}

this.argumentResolvers其中主角类RequestPartMethodArgumentResolver用来生成

public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {
    
    ...
	public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		...
	}
    
	@Nullable
	public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
		...
		return doInvoke(args);//反射调用
	}
    
	@Nullable
	protected Object doInvoke(Object... args) throws Exception {
		Method method = getBridgedMethod();
		ReflectionUtils.makeAccessible(method);
		return method.invoke(getBean(), args);
		...
	}
    
    //处理得出multipart参数，准备稍后的反射调用（@PostMapping标记的上传方法）
    protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

		MethodParameter[] parameters = getMethodParameters();
		...
		Object[] args = new Object[parameters.length];
		for (int i = 0; i < parameters.length; i++) {
			MethodParameter parameter = parameters[i];
			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
			args[i] = findProvidedArgument(parameter, providedArgs);
			if (args[i] != null) {
				continue;
			}
            //关注点1
			if (!this.resolvers.supportsParameter(parameter)) {
				throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
			}
			try {
                //关注点2
				args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
			}
			catch (Exception ex) {
				...
			}
		}
		return args;
	}
    
}

public class RequestPartMethodArgumentResolver extends AbstractMessageConverterMethodArgumentResolver {

    //对应上面代码关注点1
    @Override
	public boolean supportsParameter(MethodParameter parameter) {
        //标注@RequestPart的参数
		if (parameter.hasParameterAnnotation(RequestPart.class)) {
			return true;
		}
		else {
			if (parameter.hasParameterAnnotation(RequestParam.class)) {
				return false;
			}
			return MultipartResolutionDelegate.isMultipartArgument(parameter.nestedIfOptional());
		}
	}

    //对应上面代码关注点2
	@Override
	@Nullable
	public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest request, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		HttpServletRequest servletRequest = request.getNativeRequest(HttpServletRequest.class);
		Assert.state(servletRequest != null, "No HttpServletRequest");

		RequestPart requestPart = parameter.getParameterAnnotation(RequestPart.class);
		boolean isRequired = ((requestPart == null || requestPart.required()) && !parameter.isOptional());

		String name = getPartName(parameter, requestPart);
		parameter = parameter.nestedIfOptional();
		Object arg = null;

        //封装成MultipartFile类型的对象作参数
		Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);
		if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {
			arg = mpArg;
		}
        
        ...

		return adaptArgumentIfNecessary(arg, parameter);
	}
}

public final class MultipartResolutionDelegate {
    ...
    
	@Nullable
	public static Object resolveMultipartArgument(String name, MethodParameter parameter, HttpServletRequest request)
			throws Exception {

		MultipartHttpServletRequest multipartRequest =
				WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class);
		boolean isMultipart = (multipartRequest != null || isMultipartContent(request));

		if (MultipartFile.class == parameter.getNestedParameterType()) {
			if (!isMultipart) {
				return null;
			}
			if (multipartRequest == null) {
				multipartRequest = new StandardMultipartHttpServletRequest(request);
			}
			return multipartRequest.getFile(name);
		}
		else if (isMultipartFileCollection(parameter)) {
			if (!isMultipart) {
				return null;
			}
			if (multipartRequest == null) {
				multipartRequest = new StandardMultipartHttpServletRequest(request);
			}
			List<MultipartFile> files = multipartRequest.getFiles(name);
			return (!files.isEmpty() ? files : null);
		}
		else if (isMultipartFileArray(parameter)) {
			if (!isMultipart) {
				return null;
			}
			if (multipartRequest == null) {
				multipartRequest = new StandardMultipartHttpServletRequest(request);
			}
			List<MultipartFile> files = multipartRequest.getFiles(name);
			return (!files.isEmpty() ? files.toArray(new MultipartFile[0]) : null);
		}
		else if (Part.class == parameter.getNestedParameterType()) {
			if (!isMultipart) {
				return null;
			}
			return request.getPart(name);
		}
		else if (isPartCollection(parameter)) {
			if (!isMultipart) {
				return null;
			}
			List<Part> parts = resolvePartList(request, name);
			return (!parts.isEmpty() ? parts : null);
		}
		else if (isPartArray(parameter)) {
			if (!isMultipart) {
				return null;
			}
			List<Part> parts = resolvePartList(request, name);
			return (!parts.isEmpty() ? parts.toArray(new Part[0]) : null);
		}
		else {
			return UNRESOLVABLE;
		}
	}
    
    ...
    
}

3.2.12、错误处理-SpringBoot默认错误处理机制

Spring Boot官方文档 - Error Handling

默认规则：

  • 默认情况下，Spring Boot提供/error处理所有错误的映射
  • 机器客户端，它将生成JSON响应，其中包含错误，HTTP状态和异常消息的详细信息。对于浏览器客户端，响应一个“ whitelabel”错误视图，以HTML格式呈现相同的数据
{
  "timestamp": "2020-11-22T05:53:28.416+00:00",
  "status": 404,
  "error": "Not Found",
  "message": "No message available",
  "path": "/asadada"
}
  • 要对其进行自定义，添加View解析为error
  • 要完全替换默认行为，可以实现 ErrorController 并注册该类型的Bean定义，或添加ErrorAttributes类型的组件以使用现有机制但替换其内容。
  • /templates/error/下的4xx，5xx页面会被自动解析

3.2.13、错误处理-【源码分析】底层组件功能分析

  • ErrorMvcAutoConfiguration 自动配置异常处理规则
  • 容器中的组件：类型：DefaultErrorAttributes -> id：errorAttributes
  • public class DefaultErrorAttributes implements ErrorAttributes, HandlerExceptionResolver
    • DefaultErrorAttributes：定义错误页面中可以包含数据（异常明细，堆栈信息等）。
  • 容器中的组件：类型：BasicErrorController --> id：basicErrorController（json+白页 适配响应）
  • 处理默认 /error 路径的请求，页面响应 new ModelAndView("error", model);
    • 容器中有组件 View->id是error；（响应默认错误页）
    • 容器中放组件 BeanNameViewResolver（视图解析器）；按照返回的视图名作为组件的id去容器中找View对象。
  • 容器中的组件：类型：DefaultErrorViewResolver -> id：conventionErrorViewResolver
  • 如果发生异常错误，会以HTTP的状态码 作为视图页地址（viewName），找到真正的页面（主要作用）。
    • error/404、5xx.html
    • 如果想要返回页面，就会找error视图（StaticView默认是一个白页）。

3.2.14、错误处理-【源码流程】异常处理流程

譬如写一个会抛出异常的控制层：

@Slf4j
@RestController
public class HelloController {

    @RequestMapping("/hello")
    public String handle01(){

        int i = 1 / 0;//将会抛出ArithmeticException

        log.info("Hello, Spring Boot 2!");
        return "Hello, Spring Boot 2!";
    }
}

当浏览器发出/hello请求，DispatcherServlet的doDispatch()的mv = ha.handle(processedRequest, response, mappedHandler.getHandler());将会抛出ArithmeticException。

public class DispatcherServlet extends FrameworkServlet {
    ...
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		...
				// Actually invoke the handler.
            	//将会抛出ArithmeticException
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				applyDefaultViewName(processedRequest, mv);
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
                //将会捕捉ArithmeticException
				dispatchException = ex;
			}
			catch (Throwable err) {
				...
			}
    		//捕捉后，继续运行
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
			triggerAfterCompletion(processedRequest, response, mappedHandler,
					new NestedServletException("Handler processing failed", err));
		}
		finally {
			...
		}
	}

	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				...
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				//ArithmeticException将在这处理
                mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}
		...
	}

	protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
			@Nullable Object handler, Exception ex) throws Exception {

		// Success and error responses may use different content types
		request.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);

		// Check registered HandlerExceptionResolvers...
		ModelAndView exMv = null;
		if (this.handlerExceptionResolvers != null) {
            //遍历所有的 handlerExceptionResolvers，看谁能处理当前异常HandlerExceptionResolver处理器异常解析器
			for (HandlerExceptionResolver resolver : this.handlerExceptionResolvers) {
				exMv = resolver.resolveException(request, response, handler, ex);
				if (exMv != null) {
					break;
				}
			}
		}
		...
	
        //若只有系统的自带的异常解析器（没有自定义的），异常还是会抛出
		throw ex;
	}

}

系统自带的异常解析器：

在这里插入图片描述

  • DefaultErrorAttributes先来处理异常，它主要功能把异常信息保存到request域，并且返回null。
public class DefaultErrorAttributes implements ErrorAttributes, HandlerExceptionResolver, Ordered {
    ...
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
        this.storeErrorAttributes(request, ex);
        return null;
    }

    private void storeErrorAttributes(HttpServletRequest request, Exception ex) {
        request.setAttribute(ERROR_ATTRIBUTE, ex);//把异常信息保存到request域
    }
    ...
    
}
  • 默认没有任何解析器（上图的HandlerExceptionResolverComposite）能处理异常，所以最后异常会被抛出。
  • 最终底层就会转发/error 请求。会被底层的BasicErrorController处理。
@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {

    @RequestMapping(produces = MediaType.TEXT_HTML_VALUE)
    public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
       HttpStatus status = getStatus(request);
       Map<String, Object> model = Collections
             .unmodifiableMap(getErrorAttributes(request, getErrorAttributeOptions(request, MediaType.TEXT_HTML)));
       response.setStatus(status.value());
       ModelAndView modelAndView = resolveErrorView(request, response, status, model);
       //如果/template/error内没有4**.html或5**.html，
       //modelAndView为空，最终还是返回viewName为error的modelAndView
       return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);
    }
    
    ...
}

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    
    ...
    
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        ...
     	// Actually invoke the handler.
		mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
		...
        //渲染页面
		processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        ...
    }
    
    private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

        boolean errorView = false;
        ...
		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		...
	}
    
    protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
		...

		View view;
		String viewName = mv.getViewName();
		if (viewName != null) {
			// We need to resolve the view name.
            //找出合适error的View，如果/template/error内没有4**.html或5**.html，
            //将会返回默认异常页面ErrorMvcAutoConfiguration.StaticView
            //这里按需深究代码吧！
			view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
			...
		}
		...
		try {
			if (mv.getStatus() != null) {
				response.setStatus(mv.getStatus().value());
			}
            //看下面代码块的StaticView的render块
			view.render(mv.getModelInternal(), request, response);
		}
		catch (Exception ex) {
			...
		}
	}
    
}

@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class })
// Load before the main WebMvcAutoConfiguration so that the error View is available
@AutoConfigureBefore(WebMvcAutoConfiguration.class)
@EnableConfigurationProperties({ ServerProperties.class, ResourceProperties.class, WebMvcProperties.class })
public class ErrorMvcAutoConfiguration {
    
    ...
        
   	@Configuration(proxyBeanMethods = false)
	@ConditionalOnProperty(prefix = "server.error.whitelabel", name = "enabled", matchIfMissing = true)
	@Conditional(ErrorTemplateMissingCondition.class)
	protected static class WhitelabelErrorViewConfiguration {

        //将创建一个名为error的系统默认异常页面View的Bean
		private final StaticView defaultErrorView = new StaticView();

		@Bean(name = "error")
		@ConditionalOnMissingBean(name = "error")
		public View defaultErrorView() {
			return this.defaultErrorView;
		}

		// If the user adds @EnableWebMvc then the bean name view resolver from
		// WebMvcAutoConfiguration disappears, so add it back in to avoid disappointment.
		@Bean
		@ConditionalOnMissingBean
		public BeanNameViewResolver beanNameViewResolver() {
			BeanNameViewResolver resolver = new BeanNameViewResolver();
			resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);
			return resolver;
		}

	}     
   
    
	private static class StaticView implements View {

		private static final MediaType TEXT_HTML_UTF8 = new MediaType("text", "html", StandardCharsets.UTF_8);

		private static final Log logger = LogFactory.getLog(StaticView.class);

		@Override
		public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response)
				throws Exception {
			if (response.isCommitted()) {
				String message = getMessage(model);
				logger.error(message);
				return;
			}
			response.setContentType(TEXT_HTML_UTF8.toString());
			StringBuilder builder = new StringBuilder();
			Object timestamp = model.get("timestamp");
			Object message = model.get("message");
			Object trace = model.get("trace");
			if (response.getContentType() == null) {
				response.setContentType(getContentType());
			}
            //系统默认异常页面html代码
			builder.append("<html><body><h1>Whitelabel Error Page</h1>").append(
					"<p>This application has no explicit mapping for /error, so you are seeing this as a fallback.</p>")
					.append("<div id='created'>").append(timestamp).append("</div>")
					.append("<div>There was an unexpected error (type=").append(htmlEscape(model.get("error")))
					.append(", status=").append(htmlEscape(model.get("status"))).append(").</div>");
			if (message != null) {
				builder.append("<div>").append(htmlEscape(message)).append("</div>");
			}
			if (trace != null) {
				builder.append("<div style='white-space:pre-wrap;'>").append(htmlEscape(trace)).append("</div>");
			}
			builder.append("</body></html>");
			response.getWriter().append(builder.toString());
		}

		private String htmlEscape(Object input) {
			return (input != null) ? HtmlUtils.htmlEscape(input.toString()) : null;
		}

		private String getMessage(Map<String, ?> model) {
			Object path = model.get("path");
			String message = "Cannot render error page for request [" + path + "]";
			if (model.get("message") != null) {
				message += " and exception [" + model.get("message") + "]";
			}
			message += " as the response has already been committed.";
			message += " As a result, the response may have the wrong status code.";
			return message;
		}

		@Override
		public String getContentType() {
			return "text/html";
		}

	}
}

3.2.15、错误处理-【源码流程】几种异常处理原理

  • 自定义错误页
    • error/404.html error/5xx.html；有精确的错误状态码页面就匹配精确，没有就找 4xx.html；如果都没有就触发白页
  • @ControllerAdvice+@ExceptionHandler处理全局异常；底层是 ExceptionHandlerExceptionResolver 支持的
@Slf4j
@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler({ArithmeticException.class,NullPointerException.class})  //处理异常
    public String handleArithException(Exception e){

        log.error("异常是：{}",e);
        return "login"; //视图地址
    }
}
  • @ResponseStatus+自定义异常 ；底层是 ResponseStatusExceptionResolver ，把responseStatus注解的信息底层调用 response.sendError(statusCode, resolvedReason)，tomcat发送的/error
@ResponseStatus(value= HttpStatus.FORBIDDEN,reason = "用户数量太多")
public class UserTooManyException extends RuntimeException {

    public  UserTooManyException(){

    }
    public  UserTooManyException(String message){
        super(message);
    }
}


@Controller
public class TableController {
    
	@GetMapping("/dynamic_table")
    public String dynamic_table(@RequestParam(value="pn",defaultValue = "1") Integer pn,Model model){
        //表格内容的遍历
	     List<User> users = Arrays.asList(new User("zhangsan", "123456"),
                new User("lisi", "123444"),
                new User("haha", "aaaaa"),
                new User("hehe ", "aaddd"));
        model.addAttribute("users",users);

        if(users.size()>3){
            throw new UserTooManyException();//抛出自定义异常
        }
        return "table/dynamic_table";
    }
    
}
  • Spring自家异常如 org.springframework.web.bind.MissingServletRequestParameterException，DefaultHandlerExceptionResolver 处理Spring自家异常。
    • response.sendError(HttpServletResponse.SC_BAD_REQUEST/*400*/, ex.getMessage());
  • 自定义实现 HandlerExceptionResolver 处理异常；可以作为默认的全局异常处理规则
@Order(value= Ordered.HIGHEST_PRECEDENCE)  //优先级，数字越小优先级越高
@Component
public class CustomerHandlerExceptionResolver implements HandlerExceptionResolver {
    @Override
    public ModelAndView resolveException(HttpServletRequest request,
                                         HttpServletResponse response,
                                         Object handler, Exception ex) {

        try {
            response.sendError(511,"我喜欢的错误");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return new ModelAndView();
    }
}
  • ErrorViewResolver 实现自定义处理异常
    • response.sendError()，error请求就会转给controller。
    • 你的异常没有任何人能处理，tomcat底层调用response.sendError()，error请求就会转给controller。
    • basicErrorController 要去的页面地址是 ErrorViewResolver 。
@Controller
@RequestMapping("${server.error.path:${error.path:/error}}")
public class BasicErrorController extends AbstractErrorController {

    ...
    
	@RequestMapping(produces = MediaType.TEXT_HTML_VALUE)
	public ModelAndView errorHtml(HttpServletRequest request, HttpServletResponse response) {
		HttpStatus status = getStatus(request);
		Map<String, Object> model = Collections
				.unmodifiableMap(getErrorAttributes(request, getErrorAttributeOptions(request, MediaType.TEXT_HTML)));
		response.setStatus(status.value());
		ModelAndView modelAndView = resolveErrorView(request, response, status, model);
		return (modelAndView != null) ? modelAndView : new ModelAndView("error", model);
	}
    
    protected ModelAndView resolveErrorView(HttpServletRequest request, HttpServletResponse response, HttpStatus status,
			Map<String, Object> model) {
        //这里用到ErrorViewResolver接口
		for (ErrorViewResolver resolver : this.errorViewResolvers) {
			ModelAndView modelAndView = resolver.resolveErrorView(request, status, model);
			if (modelAndView != null) {
				return modelAndView;
			}
		}
		return null;
	}
    
    ...
    
}


@FunctionalInterface
public interface ErrorViewResolver {

	ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status, Map<String, Object> model);

}
posted @ 2022-10-28 21:18  wylja  阅读(102)  评论(0)  编辑  收藏  举报