事件监听机制

事件发布

Spring提供了两个接口实现发布事件，分别是：ApplicationEventPublisher和ApplicationEventMulticaster。

ApplicationEventPublisher源码：

package org.springframework.context;

@FunctionalInterface
public interface ApplicationEventPublisher {
    default void publishEvent(ApplicationEvent event) {
        this.publishEvent((Object)event);
    }
    // spring 4.2后支持发布任何对象作为事件
    void publishEvent(Object var1);
}

使用ApplicationEventPublisher发布事件的实例代码

@RestController
@RequestMapping("test/")
public class Test implements ApplicationContextAware {
    //ApplicationContext 实现了ApplicationEventPublisher接口，为了省事直接拿来用
    ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @RequestMapping(value = "publishEvent",method = {RequestMethod.POST})
    public Demo publishEvent(@RequestBody Demo myEvent){
        applicationContext.publishEvent(myEvent);
        return myEvent;
    }

}

关于Aware接口:Spring提供了各种aware接口用户获取不同的实例。

ApplicationEventMulticaster源码

package org.springframework.context.event;

import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;

public interface ApplicationEventMulticaster {
    // 添加监听器
    void addApplicationListener(ApplicationListener<?> var1);
    // 以bean的方式添加监听器
    void addApplicationListenerBean(String var1);
    // 移除监听器
    void removeApplicationListener(ApplicationListener<?> var1);
    // 同上
    void removeApplicationListenerBean(String var1);
   
    void removeAllListeners();
    //发布事件
    void multicastEvent(ApplicationEvent var1);
    // ResolvableType是泛型信息
    void multicastEvent(ApplicationEvent var1, @Nullable ResolvableType var2);
}

ApplicationEventMulticaster发布事件demo

@RestController
@RequestMapping("test/")
public class Test  {

    @Autowired
    MyEventListener2 myEventListener2;
    SimpleApplicationEventMulticaster simpleApplicationEventMulticaster;

   

    @RequestMapping(value = "multicastEvent",method = {RequestMethod.POST})
    public String multicastEvent(@RequestBody Demo demo){
        MyEvent myEvent = new MyEvent(demo);
        simpleApplicationEventMulticaster = new SimpleApplicationEventMulticaster();
        simpleApplicationEventMulticaster.addApplicationListener(myEventListener2);
        simpleApplicationEventMulticaster.multicastEvent(myEvent);
        return "multicastEvent succeed";
    }

}

事件监听

注解方式实现事件监听

@Component
public class MyEventListener {

    @Async
    @EventListener
    public String onMyMessage(Demo myEvent){
        System.out.println("eventListener on message:"+JSON.toJSONString(myEvent));
        return "myNewEvent";
    }
}

若返回值不为空则会被作为新的事件再次发布。

实现ApplicationListener接口监听事件

@Component
public class MyEventListener2 implements ApplicationListener<MyEvent> {

    @Override
    public void onApplicationEvent(MyEvent applicationEvent) {
        System.out.println("实现ApplicationListener方法监听事件："+applicationEvent.data);
    }
}

public class MyEvent extends ApplicationEvent {


    Object data;
    public MyEvent(Object source) {
        super(source);
        this.data = source;
    }
}