Spring的Event

只要是事件就是观察者模式,Spring中的Event也不例外,主要应用就是程序解耦,实现本质是广播的形式........屁话不多说

继承ApplicationEvent即可,但是Spring版本4.2之后不再强制要求继承ApplicationEvent,非Application的子类将被封装成PayloadApplicationEvent:

实现:

import org.springframework.context.ApplicationEvent;

public class MyEvent extends ApplicationEvent {
    //todo -----  
    private String msg;

    public MyEvent(Object source) {
        super(source);
    }

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

    public String getMsg() {
        return msg;
    }
}

编写事件推送的service实现ApplicationContextAwar接口,或者实现ApplicationEventPublisherAware接口,在需要时候根据业务场景推送事件:

实现:

@Service
public class EventProduceService implements ApplicationContextAware, ApplicationEventPublisherAware {
    //实现方式一
    private ApplicationContext applicationContext;
    //实现方式二
    private ApplicationEventPublisher applicationEventPublisher;

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

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


    
    public void sentEvent(){
        //方式一:applicationContext的推送Api可以以根据需要进行选择
        applicationContext.publishEvent(new MyEvent(this,"我是一颗小码农"));
        //方式二: applicationEventPublisher的推送Api可以以根据需要进行选择
        applicationEventPublisher.publishEvent(new MyEvent(this,"今天是20220804"));
    }
}

编写事件的处理器,交给Spring的ioc管理即可,实现有两种方式,

(1)通过@EventListener注解标注对应的事件处理器,处理器会根据参数类型自动识别事件类型的

实现:

@Configuration
public class EventConfig {
    @EventListener
    public void doWithEvent(MyEvent myEvent) {
        System.out.println("事件消息是: "+myEvent.getMsg());
    }

   @EventListener
   public void doWithEvent(BEvent myEvent) {
       System.out.println("事件消息是: "+myEvent.getMsg());
   }

    @EventListener
    public void doWithEvent(CEvent myEvent) {
        System.out.println("事件消息是: "+myEvent.getMsg());
    }
}

(2) 实现ApplicationListener接口,处理器会根据泛型类型处理事件

实现

@Component
public class EventHandler implements ApplicationListener {

    @Override
    public void onApplicationEvent(MyEvent event) {
        //todo----
        System.out.println(event.getMsg());
    }
}

Spring默认监控的事件都是同步的,实现异步事件就需要开启异步事件的支持,配置类上使用@EventListener注解开启异步支持,然后在监听器上使用@Async注解标注即可,同一个事件多个处理器可以使用@Order注解进行排序(参数越小优先级越高)

实现:

@Configuration
@EnableAsync
public class EventConfig {
    @Async
    @EventListener
    public void doWithEvent(MyEvent myEvent) {
        System.out.println("事件消息是: "+myEvent.getMsg());
    }
}


@Async//配置类已经开启异步支持
@Component
public class EventHandler implements ApplicationListener {

    @Override
    public void onApplicationEvent(MyEvent event) {
        //todo----
        System.out.println(event.getMsg());
    }
}

//todo......改天补上,困困困.....

//todo------