當(dāng)把一個(gè)事件發(fā)布到Spring提供的ApplicationContext中，被監(jiān)聽(tīng)器偵測(cè)到，就會(huì)執(zhí)行對(duì)應(yīng)的處理方法。

事件本身

事件是一個(gè)自定義的類，需要繼承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;
    }
}

事件監(jiān)聽(tīng)

基本方法是實(shí)現(xiàn)ApplicationListener接口，自定義一個(gè)監(jiān)聽(tīng)器，實(shí)現(xiàn)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("監(jiān)聽(tīng)到MyEvent事件");  
    }  
}  
...
// SpringBoot的啟動(dòng)類中添加監(jiān)聽(tīng)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（推薦）：原理就是通過(guò)掃描這個(gè)注解，創(chuàng)建監(jiān)聽(tīng)器并添加到ApplicationContext。

@Component
@Slf4j
public class MyEventHandler {

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

}

事件發(fā)布

可以通過(guò)上下文對(duì)象的發(fā)布方法ConfigurableApplicationContext::publishEvent()來(lái)發(fā)布。
也可以實(shí)現(xiàn)ApplicationEventPublisherAware接口來(lái)發(fā)布（推薦）。

@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";
    }
}

測(cè)試代碼

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

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

image

注意

如果2個(gè)事件之間是繼承關(guān)系，會(huì)先監(jiān)聽(tīng)到子類事件，處理完再監(jiān)聽(tīng)父類。

// MyEvent2 extends MyEvent

@Component
@Slf4j
public class MyEventHandler {

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

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

當(dāng)我publish一個(gè)子類事件MyEvent2時(shí)，日志如下：

image

默認(rèn)是同步事件，如要使用異步，需要開(kāi)啟異步，并使用@Async