Java 监听机制

SpringBoot 的监听机制，其实是对Java提供的事件监听机制的封装。
Java中的事件监听机制定义了以下几个角色：

• 事件：Event，继承 java.util.EventObject 类的对象
• 事件源：Source ，任意对象Object
• 监听器：Listener，实现 java.util.EventListener 接口 的对象

SpringBoot 监听机制

SpringBoot 在项目启动时，会对几个监听器进行回调，我们可以实现这些监听器接口，在项目启动时完成一些操作。
ApplicationContextInitializer、SpringApplicationRunListener、CommandLineRunner、ApplicationRunner

META-INF/spring.factories

org.springframework.context.ApplicationContextInitializer=com.release.springbootlistener.listener.MyApplicationContextInitializerorg.springframework.boot.SpringApplicationRunListener=com.release.springbootlistener.listener.MySpringApplicationRunListener

• ApplicationContextInitializer

  @Component
  public class MyApplicationContextInitializer implements ApplicationContextInitializer {@Overridepublic void initialize(ConfigurableApplicationContext applicationContext) {System.out.println("ApplicationContextInitializer....initialize");}
  }
  

• SpringApplicationRunListener

  public class MySpringApplicationRunListener implements SpringApplicationRunListener {public MySpringApplicationRunListener(SpringApplication application, String[] args) {}@Overridepublic void starting() {System.out.println("starting...项目启动中");}@Overridepublic void environmentPrepared(ConfigurableEnvironment environment) {System.out.println("environmentPrepared...环境对象开始准备");}@Overridepublic void contextPrepared(ConfigurableApplicationContext context) {System.out.println("contextPrepared...上下文对象开始准备");}@Overridepublic void contextLoaded(ConfigurableApplicationContext context) {System.out.println("contextLoaded...上下文对象开始加载");}@Overridepublic void started(ConfigurableApplicationContext context) {System.out.println("started...上下文对象加载完成");}@Overridepublic void running(ConfigurableApplicationContext context) {System.out.println("running...项目启动完成，开始运行");}@Overridepublic void failed(ConfigurableApplicationContext context, Throwable exception) {System.out.println("failed...项目启动失败");}
  }

• CommandLineRunner

  @Component
  public class MyCommandLineRunner implements CommandLineRunner {@Overridepublic void run(String... args) throws Exception {System.out.println("CommandLineRunner...run");System.out.println(Arrays.asList(args));}
  }
  

• ApplicationRunner

  /*** 当项目启动后执行run方法。*/
  @Component
  public class MyApplicationRunner implements ApplicationRunner {@Overridepublic void run(ApplicationArguments args) throws Exception {System.out.println("ApplicationRunner...run");System.out.println(Arrays.asList(args.getSourceArgs()));}
  }