Day21-springMVC

SpringMVC

回顾Servlet

环境搭建

1. 导包

   • junit

   • spring-webmvc

   • servlet-api

   • jsp-api

   • jstl

   <?xml version="1.0" encoding="UTF-8"?>
   <project xmlns="http://maven.apache.org/POM/4.0.0"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
       <modelVersion>4.0.0</modelVersion>
   ​
       <groupId>com.lsq</groupId>
       <artifactId>SpringMVC-study</artifactId>
       <packaging>pom</packaging>
       <version>1.0-SNAPSHOT</version>
       <modules>
           <module>springmvc-01</module>
       </modules>
   ​
       <properties>
           <maven.compiler.source>8</maven.compiler.source>
           <maven.compiler.target>8</maven.compiler.target>
       </properties>
   ​
       <dependencies>
           <dependency>
               <groupId>junit</groupId>
               <artifactId>junit</artifactId>
               <version>4.13.2</version>
           </dependency>
           <dependency>
               <groupId>org.springframework</groupId>
               <artifactId>spring-webmvc</artifactId>
               <version>5.2.15.RELEASE</version>
           </dependency>
           <dependency>
               <groupId>javax.servlet</groupId>
               <artifactId>servlet-api</artifactId>
               <version>2.5</version>
           </dependency>
           <dependency>
               <groupId>javax.servlet.jsp</groupId>
               <artifactId>jsp-api</artifactId>
               <version>2.2.1-b03</version>
           </dependency>
           <dependency>
               <groupId>javax.servlet</groupId>
               <artifactId>jstl</artifactId>
               <version>1.2</version>
           </dependency>
       </dependencies>
   ​
   </project>

2. 编写一个servlet类

   "add".equals(method)  //写成method.equals("add")可能会出现空指针的情况

   package com.lsq.servlet;
   ​
   import javax.servlet.ServletException;
   import javax.servlet.http.HttpServlet;
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   import java.io.IOException;
   ​
   public class HelloServlet extends HttpServlet {
       @Override
       protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
           //1.获取前端参数
           String method = req.getParameter("method");
           if (method.equals("add")) {
               req.getSession().setAttribute("msg", "执行了add方法");
           }
           if (method.equals("delete")) {
               req.getSession().setAttribute("msg", "执行了delete方法");
           }
           //2.调用业务层
           //3.视图转发或者重定向
           req.getRequestDispatcher("/WEB-INF/jsp/test.jsp").forward(req,resp);
       }
   ​
       @Override
       protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
           doGet(req, resp);
       }
   }

3. 编写xml文件

   <?xml version="1.0" encoding="UTF-8"?>
   <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
            version="4.0">
       <!--注册servlet-->
       <servlet>
           <servlet-name>hello</servlet-name>
           <servlet-class>com.lsq.servlet.HelloServlet</servlet-class>
       </servlet>
       <!--servlet的请求路径-->
       <servlet-mapping>
           <servlet-name>hello</servlet-name>
           <url-pattern>/hello</url-pattern>
       </servlet-mapping>
       <session-config>
           <session-timeout>15</session-timeout>
       </session-config>
       <welcome-file-list>
           <welcome-file>index.jsp</welcome-file>
       </welcome-file-list>
   </web-app>

4. jsp

   <%--
     Created by IntelliJ IDEA.
     User: liushaoqin
     Date: 2023/8/1
     Time: 00:54
     To change this template use File | Settings | File Templates.
   --%>
   <%@ page contentType="text/html;charset=UTF-8" language="java" %>
   <html>
   <head>
       <title>Title</title>
   </head>
   <body>
   <form action="/hello" method="post">
       <input type="text" name="method">
       <input type="submit">
   </form>
   </body>
   </html>

   <%--
     Created by IntelliJ IDEA.
     User: liushaoqin
     Date: 2023/8/1
     Time: 00:43
     To change this template use File | Settings | File Templates.
   --%>
   <%@ page contentType="text/html;charset=UTF-8" language="java" %>
   <html>
   <head>
       <title>Title</title>
   </head>
   <body>
   ${msg}
   </body>
   </html>

SpringMVC执行原理

第一个Spring+SpringMVC项目

1. 新建一个module，添加web的支持

   

   

   

2. 确定导入了SpringMVC的依赖

   

3. 配置web.xml，注册DispatchServlet

   <?xml version="1.0" encoding="UTF-8"?>
   <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
            version="4.0">
       <!--配置DispatchServlet：SpringMVC的核心，请求分发器，前端控制器-->
      <servlet>
          <servlet-name>springmvc</servlet-name>
          <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
          <init-param>
              <param-name>contextConfigLocation</param-name>
              <param-value>classpath:springmvc-servlet.xml</param-value>
          </init-param>
      </servlet>
   ​
       <!--
       在SpringMVC中 / /*
       /：只匹配所有请求，不会匹配jsp页面
       /*：匹配所有的请求，包括jsp页面
       -->
       <servlet-mapping>
           <servlet-name>springmvc</servlet-name>
           <url-pattern>/</url-pattern>
       </servlet-mapping>
   ​
   </web-app>

4. 配置springmvc-servlet.xml，注册适配器和映射器

   <?xml version="1.0" encoding="UTF-8"?>
   <beans xmlns="http://www.springframework.org/schema/beans"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xmlns:aop="http://www.springframework.org/schema/aop"
          xsi:schemaLocation="http://www.springframework.org/schema/beans
           https://www.springframework.org/schema/beans/spring-beans.xsd
           http://www.springframework.org/schema/aop
           https://www.springframework.org/schema/aop/spring-aop.xsd">
       <!--处理器映射器-->
       <bean class="org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping"/>
       <!--处理器适配器-->
       <bean class="org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter"/>
   ​
       <!--视图解析器：模版引擎 Thymeleaf Freemarker-->
       <bean id="internalResourceViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
           <!--前缀-->
           <property name="prefix" value="/WEB-INF/jsp/"/>
           <!--后缀-->
           <property name="suffix" value=".jsp"/>
       </bean>
   ​
       <bean id="/hello" class="com.lsq.controller.HelloController"/>
   </beans>

5. HelloCotroller.java

   package com.lsq.controller;
   ​
   import org.springframework.web.servlet.ModelAndView;
   import org.springframework.web.servlet.mvc.Controller;
   ​
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   ​
   public class HelloController implements Controller {
       @Override
       public ModelAndView handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception {
           ModelAndView modelAndView = new ModelAndView();
           modelAndView.addObject("msg","helloSpringMVC");
           //视图跳转
           modelAndView.setViewName("test");
           return modelAndView;
       }
   }

6. test.jsp

   <%--
     Created by IntelliJ IDEA.
     User: liushaoqin
     Date: 2023/8/1
     Time: 17:42
     To change this template use File | Settings | File Templates.
   --%>
   <%@ page contentType="text/html;charset=UTF-8" language="java" %>
   <html>
   <head>
       <title>Title</title>
   </head>
   <body>
   ${msg}
   </body>
   </html>

7. 启动tomcat提示404

   • 解决方案1：

   1. 打开项目结构

   2. 选择工件

   3. 找到当前模块选中，查看WEB-INF下是否有lib目录，若没有则新建

      

   4. 选择lib新建库文件，把包全选导入

      

   • 解决方案2:

     • 在web.xml文件中设置默认启动的jsp,在配置文件中加上下面的代码

       <welcome-file-list>
               <welcome-file>index.jsp</welcome-file>
       </welcome-file-list> 

SpringMVC项目配置（不用之前的Servlet）

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
​
    <!--配置DispatchServlet：SpringMVC的核心，请求分发器，前端控制器-->
    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc-servlet.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
​
    <!--
    在SpringMVC中 / /*
    /：只匹配所有请求，不会匹配jsp页面
    /*：匹配所有的请求，包括jsp页面
    -->
    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
​
</web-app>

配置springmvc-servlet.xml，不再需要注册适配器和映射器

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/aop
        https://www.springframework.org/schema/aop/spring-aop.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/mvc
        https://www.springframework.org/schema/mvc/spring-mvc.xsd">
​
    <context:component-scan base-package="com.lsq.controller"/>
    <mvc:default-servlet-handler/>
    <mvc:annotation-driven/>
​
    <!--视图解析器：模版引擎 Thymeleaf Freemarker-->
    <bean id="internalResourceViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <!--前缀-->
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <!--后缀-->
        <property name="suffix" value=".jsp"/>
    </bean>
​
​
</beans>

controller

package com.lsq.controller;
​
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;
​
@Controller
public class HelloController {
    @RequestMapping("/hello")
    public String hello(Model model){
        model.addAttribute("msg","springmvcAnnotation");
        return "hello";
    }
}

启动页面jsp

<%--
  Created by IntelliJ IDEA.
  User: liushaoqin
  Date: 2023/8/2
  Time: 04:46
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
${msg}
</body>
</html>

Restful风格

1. SpringMVC可以使用@PathVariable注解，让方法的值对应绑定一个URL模版变量上

2. 使用restful操作资源：可以通过不同的请求方式来实现不同的效果

   • http://127.0.0.1/item/1 查询 GET

   • http://127.0.0.1/item 新增 POST

   • http://127.0.0.1/item 更新 PUT

   • http://127.0.0.1/item/1 删除 DELETE

3. 使用方式（默认使用get方式）

   • @Controller
     public class HelloController{
     ​
         @RequestMapping("/hello/{a}{b}")
         public String test(@PathVariable int a,@PathVariable int b, Model model){
             int result=a+b;
             model.addAttribute("msg","结果为"+result);
             return "hello";
         }
     }

   • @Controller
     public class HelloController{
     ​
         @RequestMapping(value = "/hello/{a}{b}",method = POST)
         public String test(@PathVariable int a,@PathVariable int b, Model model){
             int result=a+b;
             model.addAttribute("msg","结果为"+result);
             return "hello";
         }
     }

   • @Controller
     public class HelloController{
     ​
         @GetMapping("/hello/{a}{b}")
         public String test(@PathVariable int a,@PathVariable int b, Model model){
             int result=a+b;
             model.addAttribute("msg","结果为"+result);
             return "hello";
         }
     }

   SpringMVC：结果跳转方式

   扩展：转发和重定向

   　转发相当于，张三向你借钱，但是你兜里没钱，所以你去找李四借到钱之后借给张三。对于张三而言并不知道你的钱是和李四借的。

   　重定向相当于，张三向你借钱，你兜里没钱，你告诉他李四有钱，所以张三再次去找李四借钱。

   1. 重定向访问服务器两次，转发只访问服务器一次。

   2. 转发页面的URL不会改变，而重定向地址会改变

   3. 转发只能转发到自己的web应用内，重定向可以重定义到任意资源路径

   4. 转发相当于服务器跳转，相当于方法调用，在执行当前文件的过程中转向执行目标文件，两个文件(当前文件和目标文件)属于同一次请求，前后页 共用一个request，可以通过此来传递一些数据或者session信息，request.setAttribute()和 request.getAttribute()。而重定向会产生一个新的request，不能共享request域信息与请求参数

   5. 由于转发相当于服务器内部方法调用，所以转发后面的代码仍然会执行(转发之后记得return)；重定向代码执行之后是方法执行完成之后进行重定向操作，也就是访问第二个请求，如果是方法的最后一行进行重定向那就会马上进行重定向(重定向也需要return)。

   6. 无论是RequestDispatcher.forward方法，还是HttpServletResponse.sendRedirect方法，在调用它们之前，都不能有内容已经被实际输出到了客户端。如果缓冲区中已经有了一些内容，这些内容将被从缓冲区中移除。

   通过SpringMVC来实现转发和重定向-有视图解析器，默认进行转发

   重定向，不需要视图解析器

   @Controller
   public class HelloController{
   ​
       @RequestMapping("/hello")
       public String test(){
           return "redirect:/hello.jsp";
       }
   }

   解决SprinMVC乱码问题

   <!--配置springMVC的乱码过滤-->
       <filter>
           <filter-name>encoding</filter-name>
           <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
           <init-param>
               <param-name>encoding</param-name>
               <param-value>utf-8</param-value>
           </init-param>
       </filter>
       
       <filter-mapping>
           <filter-name>encoding</filter-name>
           <url-pattern>/*</url-pattern>
       </filter-mapping>

   json解析工具(jackson)

   导入jar包

   <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
   <dependency>
       <groupId>com.fasterxml.jackson.core</groupId>
       <artifactId>jackson-databind</artifactId>
       <version>2.15.2</version>
   </dependency>

   解决json乱码问题

   <!--JSON乱码问题配置-->
       <mvc:annotation-driven>
           <mvc:message-converters register-defaults="true">
               <bean class="org.springframework.http.converter.StringHttpMessageConverter">
                   <constructor-arg value="UTF-8"/>
               </bean>
               <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                   <property name="objectMapper">
                       <bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
                           <property name="failOnEmptyBeans" value="false"/>
                       </bean>
                   </property>
               </bean>
           </mvc:message-converters>
       </mvc:annotation-driven>

   json对于日期不使用时间戳显示

   

   纯java方式对于日期不使用时间戳显示

   

Json交互处理

导入依赖

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8</version>
</dependency>

解决json乱码问题,配置spring-mvc.xml

<!--JSON乱码问题配置-->
    <mvc:annotation-driven>
        <mvc:message-converters register-defaults="true">
            <bean class="org.springframework.http.converter.StringHttpMessageConverter">
                <constructor-arg value="UTF-8"/>
            </bean>
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                <property name="objectMapper">
                    <bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
                        <property name="failOnEmptyBeans" value="false"/>
                    </bean>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

FastJson

可以方便的实现json对象与JavaBean对象的转换，实现JavaBean对象与json字符串的转换，实现json对象与json字符串的转换

导入依赖

 <dependency>
       <groupId>com.alibaba</groupId>
       <artifactId>fastjson</artifactId>
       <version>2.0.32</version>
</dependency>

fastjson 三个主要的类：

• JSONObject 代表 json 对象

• JSONArray 代表 json 对象数组

• JSON代表 JSONObject和JSONArray的转化

工具类

package com.kuang.controller;
 
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.kuang.pojo.User;
 
import java.util.ArrayList;
import java.util.List;
 
public class FastJsonDemo {
    public static void main(String[] args) {
        //创建一个对象
        User user1 = new User("秦疆1号", 3, "男");
        User user2 = new User("秦疆2号", 3, "男");
        User user3 = new User("秦疆3号", 3, "男");
        User user4 = new User("秦疆4号", 3, "男");
        List<User> list = new ArrayList<User>();
        list.add(user1);
        list.add(user2);
        list.add(user3);
        list.add(user4);
 
        System.out.println("*******Java对象 转 JSON字符串*******");
        String str1 = JSON.toJSONString(list);
        System.out.println("JSON.toJSONString(list)==>"+str1);
        String str2 = JSON.toJSONString(user1);
        System.out.println("JSON.toJSONString(user1)==>"+str2);
 
        System.out.println("\n****** JSON字符串 转 Java对象*******");
        User jp_user1=JSON.parseObject(str2,User.class);
        System.out.println("JSON.parseObject(str2,User.class)==>"+jp_user1);
 
        System.out.println("\n****** Java对象 转 JSON对象 ******");
        JSONObject jsonObject1 = (JSONObject) JSON.toJSON(user2);
        System.out.println("(JSONObject) JSON.toJSON(user2)==>"+jsonObject1.getString("name"));
 
        System.out.println("\n****** JSON对象 转 Java对象 ******");
        User to_java_user = JSON.toJavaObject(jsonObject1, User.class);
        System.out.println("JSON.toJavaObject(jsonObject1, User.class)==>"+to_java_user);
    }
}