springboot(四)--spring事件监听、自定义事件

如题，本篇我们介绍下spring事件监听以及自定义事件。 

一、spring中内置的四种事件

事件是spring中非常重要的一种异步通知机制，在spring框架中就内置了容器事件，如ContextStartedEvent（启动） 、ContextStoppedEvent（停止）、ContextRefreshedEvent（刷新）、ContextClosedEvent（关闭），它们都继承自ApplicationEvent对象，我们编写的事件监听器类时需要实现ApplicationListener 接口，然后重写onApplicationEvent(event)方法即可。

注意 ：ContextStartedEvent、ContextStoppedEvent 这两种事件监听器，笔者在实际中配置了后好像并不起作用，我们可以用ContextRefreshedEvent、ContextClosedEvent分别代替代替前面二者。

当然除了上面的几种，我们还可以自定义事件，以及自定义事件处理器。

SpringStartedListener.java

package com.tingcream.springWeb.spring.eventListener;

 
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextStartedEvent;
import org.springframework.stereotype.Component;

@Component
public class SpringStartedListener implements ApplicationListener<ContextStartedEvent>{
	@Override
	public void onApplicationEvent(ContextStartedEvent event) {
		System.out.println("============SpringStartedListener 执行=========== ");
	}
}

SpringStoppedListener.java 

package com.tingcream.springWeb.spring.eventListener;

 
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextStoppedEvent;
import org.springframework.stereotype.Component;

@Component
public class SpringStoppedListener implements ApplicationListener<ContextStoppedEvent>{
	
	@Override
	public void onApplicationEvent(ContextStoppedEvent event) {
	 
		System.out.println("============SpringStoppedListener 执行=========== ");
		
	}

}

SpringRefreshedListener.java

package com.tingcream.springWeb.spring.eventListener;

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Component;

import com.tingcream.springWeb.common.SpringContextHelper;
import com.tingcream.springWeb.spring.event.MyAppEvent;

@Component
public class SpringRefreshedListener implements ApplicationListener<ContextRefreshedEvent>{

	@Override
	public void onApplicationEvent(ContextRefreshedEvent event) {
		System.out.println("============SpringRefreshedListener 执行=========== ");
		
	}

}

SpringClosedListener.java

package com.tingcream.springWeb.spring.eventListener;

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextClosedEvent;
import org.springframework.stereotype.Component;
 
@Component
public class SpringClosedListener  implements ApplicationListener<ContextClosedEvent>{

	@Override
	public void onApplicationEvent(ContextClosedEvent event) {
	 
		System.out.println("============SpringClosedListener 执行=========== ");
	}

}

二、spring中自定义事件及事件处理

1、编写自定义事件类  

    MyAppEvent.java

package com.tingcream.springWeb.spring.event;
 
import org.springframework.context.ApplicationEvent;
 
/**
 * 自定义事件对象
 * @author jelly
 *
 */
public class MyAppEvent  extends ApplicationEvent{  
    private static final long serialVersionUID = 1L;
    
    public MyAppEvent(Object source) {
        super(source);
    }
}

2、编写自定义事件监听器

MyAppEventListener.java

package com.tingcream.springWeb.spring.eventListener;

import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;

import com.tingcream.springWeb.spring.event.MyAppEvent;

/**
 * 自定义事件MyAppEvent的监听器
 * @author jelly
 *
 */
@Component
public class MyAppEventListener  implements ApplicationListener<MyAppEvent>{

	@Override
	public void onApplicationEvent(MyAppEvent event) {
		System.out.println("MyAppEventListener监听到MyAppEvent事件发生");
		System.out.println("事件source:"+event.getSource());//时间源对象
		System.out.println("事件timestamp:"+event.getTimestamp());
		System.out.println("事件class:"+event.getClass());
	 
	}

}

3、在spring容器中触发自定义事件

这里笔者是在spring容器启动（刷新）时自动触发一次该事件，当然实际业务中应当是在完成某个操作或任务后，在适当的时机触发该事件，如消息推送、日志通知等场景。

SpringRefreshedListener.java

package com.tingcream.springWeb.spring.eventListener;

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.stereotype.Component;

import com.tingcream.springWeb.common.SpringContextHelper;
import com.tingcream.springWeb.spring.event.MyAppEvent;

@Component
public class SpringRefreshedListener implements ApplicationListener<ContextRefreshedEvent>{

	@Override
	public void onApplicationEvent(ContextRefreshedEvent event) {
		System.out.println("============SpringRefreshedListener 执行=========== ");
		SpringContextHelper.getApplicationContext().publishEvent(new MyAppEvent("这是一段事件消息"));
	}

}

SpringContextHelper.java 

package com.tingcream.springWeb.common;
 
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
 
/**
* Spring 容器上下文辅助类
* @author jelly
*
*/
@Component
public class SpringContextHelper implements ApplicationContextAware {
     
      private static ApplicationContext applicationContext; 
       
      @Override 
      public void setApplicationContext(ApplicationContext applicationContext) 
              throws BeansException { 
          SpringContextHelper.applicationContext = applicationContext; 
      } 
         
      /**
       * 获取spring容器的 applicationContext 上下文对象
       * @return
       */
      public static ApplicationContext getApplicationContext(){ 
          return applicationContext; 
      } 
         
      public static Object getBean(String name){ 
          return applicationContext.getBean(name); 
      } 
       /**
        * 从spring 上下文中获取bean
        * @param name
        * @param requiredClass
        * @return
        */
      public static  T getBean(String name, Class  requiredClass){ 
          return applicationContext.getBean(name, requiredClass); 
      } 
      public  static  T getBean(Class requiredType){
       return applicationContext.getBean(requiredType);
      }
  
     
}

-------------------- 

注:  事件监听的处理除了采用XxxListener方式，还可以XxxHandler的方式，在handler中使用@EventListener标记方法为一个事件处理的方法即可。Listner和Handler只能选用其中一种方式，若两种方式在项目中都存在，在Listener方式生效，Handler方式无效。例如，上面的spring容器的4种内置事件监听器类可以写到一个handler类中。

 SpringContextEventHandler.java

package com.tingcream.springWeb.spring.eventListener;
 
import org.springframework.context.event.ContextClosedEvent;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.context.event.ContextStartedEvent;
import org.springframework.context.event.ContextStoppedEvent;
import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;
 
import com.tingcream.springWeb.common.SpringContextHelper;
import com.tingcream.springWeb.spring.event.MyAppEvent;
 
 
@Component
public class SpringContextEventHandler {
     
     @EventListener
     public void stopped(ContextStoppedEvent event){
       System.out.println("SpringContextEventHandler stopped执行");
     }
      
     @EventListener
     public void started(ContextStartedEvent event){
         System.out.println("SpringContextEventHandler started执行");
     }
      
     @EventListener
     public void refreshed(ContextRefreshedEvent event){
         System.out.println("SpringContextEventHandler refreshed执行");
          
            SpringContextHelper.getApplicationContext().publishEvent(new MyAppEvent("这是一段事件消息"));
          
     }
     @EventListener
     public void closed(ContextClosedEvent event){
         System.out.println("SpringContextEventHandler closed执行");
     }
 
}