SpringBoot（三）手写starter pom自动配置

思想：主要是EnableAutoConfiguration在启动的时候会扫描spring.factories并加载

1在resource下面新建META-INF/spring.factories

2在spring.factories中添加自动装载的类

3其他项目引用既OK

1.新建一个starter的Maven项目A，pom文件修改

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example.start</groupId>
    <artifactId>spring-boot-starter-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
    <!--支持读取配置文件属性-->
      <dependency>
           <groupId>org.springframework.boot</groupId>
          <artifactId>spring-boot-configuration-processor</artifactId>
          <optional>true</optional>
      </dependency>

  <!--需要改jar 才会自动加载enableautoconfiguration-->

        <dependency>

            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

2.新建resource文件,META-INF/spring.factories文件

多个可这样写：（\表示换行可读取到属性）（，多个属性分割）

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  com.example.start.demo.service.MyHelloConfiguration,\
com.example.start.demo.service.MyHelloConfiguration

3.新建MyHelloConfiguration配置类

@Configuration
public class MyHelloConfiguration {   

   //当不存在HelloService时加载
    @Bean
    @ConditionalOnMissingBean(HelloService.class)
    public HelloService test() {

        HelloService helloService = new HelloService();
        helloService.setMsg("world");
        return helloService;
    }
}

public class HelloService {

    private String msg;

    public void setMsg(String msg) {
        this
                .msg = msg;
    }

    public String sayHello() {
        return "hello" + msg;
    }
}

4.在IDEA中Maven下执行install将jar包发布到本地仓库

5在项目B中引入项目A新建的spring-boot-starter-demo.jar

   <dependency>
            <groupId>com.example.start</groupId>
            <artifactId>spring-boot-starter-demo</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>

6项目B引用测试结果：

项目B调用项目A的service

启动项目B设置application.properties文件debug=true,启动输出结果：

测试运行结果：