当把一个事件发布到Spring提供的ApplicationContext中，被监听器侦测到，就会执行对应的处理方法。

事件本身

事件是一个自定义的类，需要继承Spring提供的ApplicationEvent。

@Data
public class MyEvent extends ApplicationEvent {
    private String msg;

    public MyEvent(Object source, String msg) {
        super(source);
        this.msg = msg;
    }
}

事件监听

基本方法是实现ApplicationListener接口，自定义一个监听器，实现onApplicationEvent()方法，然后添加到ApplicationContext。
比如：

public class MyListener implements ApplicationListener<MyEvent> {  

    @Override  
    public void onApplicationEvent(MyEvent event) {  
        System.out.print("监听到MyEvent事件");  
    }  
}  
...
// SpringBoot的启动类中添加监听器
        public static void main(String[] args) {
        SpringApplication application = new SpringApplication(MyApplication.class);
        application.addListeners(new MyListener());
        application.run(args);
    }

也可以使用注解@EventListener（推荐）：原理就是通过扫描这个注解，创建监听器并添加到ApplicationContext。

@Component
@Slf4j
public class MyEventHandler {

    @EventListener
    public void handleEvent(MyEvent event) {
        log.info("------------处理事件：{}", event.getMsg());
        try {
            Thread.sleep(5 * 1000L);
            log.info("事件1(5s)处理完成");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

事件发布

可以通过上下文对象的发布方法ConfigurableApplicationContext::publishEvent()来发布。
也可以实现ApplicationEventPublisherAware接口来发布（推荐）。

@Component
@Slf4j
public class EventService implements ApplicationEventPublisherAware {
    public ApplicationEventPublisher publisher;

    @Override
    public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
        this.publisher = applicationEventPublisher;
    }

    public String doEventWork(String msg) {
        log.info("------------publish event:" + msg);
        MyEvent event = new MyEvent(this, msg);
        publisher.publishEvent(event);
        return "OK";
    }
}

测试代码

@SpringBootTest
@RunWith(SpringRunner.class)
public class EventServiceTest {
    @Autowired
    private EventService service;

    @Test
    public void eventTest() {
        String msg="Java Code";
        service.doEventWork(msg);
    }
}

注意

如果2个事件之间是继承关系，会先监听到子类事件，处理完再监听父类。

// MyEvent2 extends MyEvent

@Component
@Slf4j
public class MyEventHandler {

    @EventListener
    public void handleEvent(MyEvent event) {
        log.info("------------处理事件：{}", event.getMsg());
        try {
            Thread.sleep(5 * 1000L);
            log.info("事件1(5s)处理完成");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @EventListener
    public void handleEvent2(MyEvent2 event) {
        log.info("------------处理事件2：{}", event.getMsg());
        try {
            Thread.sleep(10 * 1000L);
            log.info("事件2(10s)处理完成");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

当我publish一个子类事件MyEvent2时，日志如下：