springboot中的事件

官网对springboot事件的描述

springboot中事件的发布顺序（发送优先级从高到底）

• ApplicationStartingEvent在运行开始时发送 ，但在进行任何处理之前（侦听器和初始化程序的注册除外）发送
• ApplicationEnvironmentPreparedEvent当被发送Environment到中已知的上下文中使用，但是在创建上下文之前
• ApplicationContextInitializedEvent在ApplicationContext准备好且已调用ApplicationContextInitializers之后但任何bean定义未加载之前发送
• ApplicationPreparedEvent在刷新开始之前但在加载bean定义之后发送
• ApplicationStartedEvent上下文已被刷新后发送，但是任何应用程序和命令行亚军都被调用前
• ApplicationReadyEvent在所有的命令行应用启动后发送此事件，可以处理请求

  ps:这里的命令行引用主要是指扩展了ApplicationRunner和CommandLineRunner的实现

• ApplicationFailedEvent如果在启动时异常发送

自定义扩展事件或监听springboot事件方法

前提：需要等待ApplicationContext已经初始化完成才能通过其发送事件

• 自定义事件

/**
 * @Author xf
 * @Description 事件（消息）
 * @Date 2019/12/6 16:41
 **/
public class MessageEvent extends ApplicationEvent {
    public MessageEvent(Object source) {
        super(source);
    }
}

• 自定义监听器
  • 实现方式1:通过@EventListener指定需要监听的事件，常用

    /**
     * @Author xf
     * @Description 事件监听
     * @Date 2019/12/6 16:42
     **/
    @Component
    public class MyListener {
        @EventListener(value = MessageEvent.class)
        public void listener(Object object){
            System.out.println("MyListener  = " + object);
        }
    }
    

  • 实现方式2：通过实现EventListener

    /**
     * @Author xf
     * @Description 刷新事件监听
     * @Date 2019/12/6 17:05
     **/
     @Component
    public class RefreshEventListener implements ApplicationListener {
        @Override
        public void onApplicationEvent(ApplicationEvent applicationEvent) {
            if(applicationEvent instanceof MessageEvent){
                final MessageEvent messageEvent = (MessageEvent) applicationEvent;
                System.out.println("(RefreshEventListener ) = " + messageEvent);
            }
        }
    }
    

  • 通过spring.factories方法扩展，这个方法不太合适用在这里，可读性不高,与上一个实现方式的区别就是去掉了注解@Component。放在spring.factories内让spring进行初始化.spring在初始化所有扩展spring.factories的内容时一并初始化。这种方式是自定义spring-boot-starter-xxx.jar的时候常用的方法。

    public class SpringFactoriesEventListener implements ApplicationListener {
        @Override
        public void onApplicationEvent(ApplicationEvent applicationEvent) {
            if(applicationEvent instanceof MessageEvent){
                final MessageEvent messageEvent = (MessageEvent) applicationEvent;
                System.out.println("(SpringFactoriesEventListener ) = " + messageEvent);
            }
        }
    }
    

    添加META-INF文件夹，并新建spring.factories文件，添加如下内容

    org.springframework.context.ApplicationListener=com.xfc.transactional.transactional.listener.SpringFactoriesEventListener
    

最后看一下运行结果

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.2.1.RELEASE)

2019-12-06 18:12:36.212  INFO 620792 --- [           main] c.x.t.t.TransactionalApplication         : Starting TransactionalApplication on chenxingfei with PID 620792 (D:\personal-workspace\transactional\target\classes started by mintq in D:\personal-workspace\transactional)
2019-12-06 18:12:36.218  INFO 620792 --- [           main] c.x.t.t.TransactionalApplication         : No active profile set, falling back to default profiles: default
2019-12-06 18:12:39.730  INFO 620792 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2019-12-06 18:12:39.759  INFO 620792 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-12-06 18:12:39.760  INFO 620792 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.27]
2019-12-06 18:12:39.972  INFO 620792 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-12-06 18:12:39.972  INFO 620792 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 3484 ms
2019-12-06 18:12:40.987  INFO 620792 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-12-06 18:12:41.748  INFO 620792 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2019-12-06 18:12:41.757  INFO 620792 --- [           main] c.x.t.t.TransactionalApplication         : Started TransactionalApplication in 7.269 seconds (JVM running for 8.432)
(MyListener) = com.xfc.transactional.transactional.event.MessageEvent[source=我发布事件了]
(SpringFactoriesEventListener) = com.xfc.transactional.transactional.event.MessageEvent[source=我发布事件了]
(RefreshEventListener) = com.xfc.transactional.transactional.event.MessageEvent[source=我发布事件了]

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