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Spring Boot FAQ

eclipse 在marketPlace安装lombok, springtool4, dbeaver,docker tooling

1. tomcat的端口,数据连接这些都存在resourcces/application.yml里

Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.

server:
  port: 8082

spring:
 datasource:
  driverClassName: com.mysql.cj.jdbc.Driver
  url: jdbc:mysql://localhost:3307/test?useSSL=false&useUnicode=true&characterEncoding=utf8
  username: root
  password: root

2. 自动导入点击File—>Settings .Editor—>General—>Auto Import IDEA默认自动导入的快捷键是：Alt+Enter

3. 未配置 SQL 方言。 idea->File->Settings->Languages & Frameworks->SQL Dialects

4. 不建议使用字段注入. 但这个写法很省事, Spring中为什么不建议使用字段注入 - EchoLv - 博客园 (cnblogs.com)

5. @SpringBootApplication 是一个配置类,它会自动扫描所有Spring Bean( 由Spring框架IOC创建的对象),

SpringBootApplication is a configuration class. It then begins autoscanning all the classes on the Java classpath for other Spring beans.

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

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args); //返回一个Spring ApplicationContext 对象。


    }

}

A Spring bean is an object that the Spring framework manages at run time with the Inversion of Control (IoC) container.

These are created and added to a “repository of objects” so you can get them later.

只有在容器中的组件，才会拥有 SpringBoot 提供的强大功能。首先就要保证该对 JavaBean 对象在 IoC 容器中，所以需要用到 @Component 注解来添加组件到容器中。

Spring容器来说，当我们把一个Bean标记为@Component后，它就会自动为我们创建一个单例（Singleton)

还有一种Bean，我们每次调用getBean(Class)，容器都返回一个新的实例，这种Bean称为Prototype（原型），它的生命周期显然和Singleton不同。声明一个Prototype的Bean时，需要添加一个额外的@Scope注解：

@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)

@ConfigurationProperties(prefix = "person") 从yml文件读取时间,会默认yml文件的时间是加了时区的, 当你打印出来默认会改成GMT时间

yml文件

person:
  lastName: 张三
  age: 18
  boss: false
  birth: 1990/12/12
  maps: { k1: v1,k2: 12 }
  lists:
    ‐ lisi
    ‐ zhaoliu
  dog:
    name: 迪迪
    age: 5

在网页JSON输出

{"lastName":"张三","age":18,"boss":false,"birth":"1990-12-11T16:00:00.000+0000","maps":{"k1":"v1","k2":12},"lists":["‐ lisi ‐ zhaoliu"],"dog":{"name":"迪迪","age":"5"}}

6. eclipse的自动完成的快捷键是输入字母后按"ALT"+'/'

7. 切换配置文件添加 4 个配置文件：application.yml：默认配置

application-dev.yml：开发环境配置
application-test.yml：测试环境配置
application-prod.yml：生产环境配置

在application.yml加上下面这段,切换到prod环境 Log会显示 c.f.helloworld.HelloworldApplication : The following profiles are active: prod

spring:
#切换配置
 profiles:
  active: prod #激活开发环境配置

Maven 打包成jar包后(Maven Clean,Maven install),可以用命令行参数--spring.profiles.active=dev 来指定版本

C:\\spring-boot-study-helloworld\target>java -jar helloworld-0.0.1-SNAPSHOT.jar --spring.profiles.active=dev

打包生成2个文件

.jar.original 是普通jar包，不包含依赖
.jar 是可执行jar包，包含了pom中的所有依赖，可以直接用java -jar 命令执行
如果是部署，就用.jar
如果是给别的项目用，就要给.jar.original这个包

8. maven 安装dockerfile-maven-plugin ,可以指定image的名字,tag, 直接打包成docker Image, 根目录有Dockerfile和docker-compose.yml, maven build就能自动打包并上传到dockerHub(前提是你注册登录了账号)

docker run -p 8080:8080 ostock/licensing-service:0.0.1-SNAPSHOT

9. 强大的lombok注解@Getter @Setter @ToString

10. Maven的仓库地址是。http://mvnrepository.com/ 比如我们要安装某个jar包, 到这个网址查找,它有一段dependency的代码,复制到POM.xml里就可以了, 参考这个

Maven 下载地址要改成阿里云的, 在这个目录新建一个文件 c:\users\[用户名]\..m2\setting.xml ,写如下的内容. 不然下载太慢了.我update一下要半个小时

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

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">


<pluginGroups>
</pluginGroups>

<proxies>
</proxies>

<servers>
</servers>

<mirrors>
<mirror>
<id>aliyun</id>
<name>aliyun Maven</name>
<mirrorOf>*</mirrorOf>
<url>https://maven.aliyun.com/repository/public/</url>
</mirror>
</mirrors>

<profiles>
</profiles>

<activeProfiles>
</activeProfiles>
</settings>

@PostMapping() 注解这样写,会出现 405错误方法不被允许 (Method not allowed)

要写成@PostMapping, 或者@PostMapping("xxxxx")

@RequestBody最多只能有一个，而@RequestParam()可以有多个。
前端传递如果是 json 格式的数据，不是Form, 我们要传入的参数是一个对象，那就必须使用 @RequestBody。

In Spring MVC, "request parameters" map to query parameters, form data, and parts in multipart requests. This is because the Servlet API combines query parameters and form data into a single map called "parameters", and that includes automatic parsing of the request body.

Eclipse 快速找到类对应的包名, 要点[Link with Editor]

Java String转Date new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse("2019-01-03 10:59:27")

CRUD RESTful 测试

package com.example.springdemo;

import static org.assertj.core.api.AssertionsForClassTypes.assertThat;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.util.Assert;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;

import com.example.springdemo.model.User;


@SpringBootTest(classes = DemoApplication.class, webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class UserControllerTest {
    @Autowired
    private TestRestTemplate template;
    private final Logger logger = LoggerFactory.getLogger(UserControllerTest.class);
    
    private int GetAllUser() throws Exception
    {
            String url ="/api/user/users";
              ResponseEntity<String> response = template.getForEntity(url, String.class);
            HttpStatus statusCode = response.getStatusCode();    
            assertThat(statusCode).isEqualTo(HttpStatus.OK);
            
            JSONArray users = new JSONArray(response.getBody());
            int prevCnt = users.length();
            
            logger.info(users.length()+" user records");
            return prevCnt;
    }
    @Test
    public void CRUD_ok() throws Exception {
        
        //先查原来有多少个记录
        int prevCnt =GetAllUser();        
        assertThat(prevCnt).isGreaterThanOrEqualTo(1);
        
        //增加一个
        String url = "/api/user/";
        HttpHeaders headers = new HttpHeaders();
        MediaType type = MediaType.APPLICATION_JSON;
        headers.setContentType(type);
        headers.add("Accept", MediaType.APPLICATION_JSON.toString());

        // Object user = new User(9999,"JUnit Test","123456",new SimpleDateFormat("yyyy-MM-dd").parse("2022-2-1"),1);
        Map<String, String> requestBody = new HashMap<String,String>();
       
        requestBody.put("id", "9999");
        requestBody.put("userName", "123");
        requestBody.put("password", "123456");        
        requestBody.put("sex", "1");
        HttpEntity<Map<String, String>> requestEntity = new HttpEntity<Map<String, String>>(requestBody, headers);
        ResponseEntity<String> response= template.postForEntity(url, requestEntity,String.class);
        HttpStatus statusCode = response.getStatusCode();    
        assertThat(statusCode).isEqualTo(HttpStatus.OK);
        int postCnt =GetAllUser();       
        assertThat(postCnt).isEqualTo(prevCnt+1);
        
        //更新内容
        url = "/api/user/9999";
        requestBody.put("userName", "JUnit");
        requestEntity = new HttpEntity<Map<String, String>>(requestBody, headers);        
        response=template.exchange(url,HttpMethod.PUT,requestEntity,String.class);
        statusCode = response.getStatusCode();    
        assertThat(statusCode).isEqualTo(HttpStatus.OK);
        
        //https://blog.csdn.net/justin_bob/article/details/103019115

        
        //删除内容
        
        url = "/api/user/9999";
        response=template.exchange(url,HttpMethod.DELETE,requestEntity,String.class);
      //template.delete("api/user/9999");
        statusCode = response.getStatusCode();    
        assertThat(statusCode).isEqualTo(HttpStatus.OK);
    }
    
}

连接别的机器上的kafka,出现下面错误

Connection to node 1 (localhost/127.0.0.1:9092) could not be established. Broker may not be available.

但application.yml配置的不是本地127.0.0.1地址, 这个就要改kafka的 advertised.listeners

# 允许外部端口连接                                            
listeners=PLAINTEXT://0.0.0.0:9092  
# 外部代理地址                                                
advertised.listeners=PLAINTEXT://121.201.64.12:9092

Kafka连接服务器出现:Connection to node 1 (localhost/127.0.0.1:9092) could not be established

SLF4J 多个Binding如何处理？

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/C:/Users/user/.m2/repository/ch/qos/logback/logback-classic/1.2.11/logback-classic-1.2.11.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/C:/Users/user/.m2/repository/org/slf4j/slf4j-reload4j/1.7.36/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [ch.qos.logback.classic.util.ContextSelectorStaticBinder]