《Pro Spring》学习笔记之ApplicationContext的事件机制

ApplicationContext的另一个特性是能够将自己作为代理发布和接受事件。事件是个继承ApplicationEvent的类，而后者本身又继承了java.util.EventObject ,是要实现了ApplicationListener接口,任何bean都能监听到事件,在进行配置时候,ApplicationContext会自动把实现该接口的bean注册位监听者,事件通过ApplicationContext.publishEvent()发布,代码如下:

MessageEvent.java

 

package  ch5.applicationContext.Event;

import  org.springframework.context.ApplicationEvent;

public   class  MessageEvent  extends  ApplicationEvent  ... {
  private String msg;
  public MessageEvent(Object source,String msg)...{
      super(source);
      this.msg=msg;
  }
public String getMsg() ...{
    return msg;
}

public void setMsg(String msg) ...{
    this.msg = msg;
}
  
}

 MessageEventListener.java

 

package  ch5.applicationContext.Event;

import  org.springframework.context.ApplicationEvent;
import  org.springframework.context.ApplicationListener;

public   class  MessageEventListener  implements  ApplicationListener  ... {

    public void onApplicationEvent(ApplicationEvent event) ...{
       if(event instanceof MessageEvent)...{
           MessageEvent msgevent=(MessageEvent)event;
           System.out.println("recieve:"+msgevent.getMsg());
       }
    }

}

 

Publisher.java

 

package  ch5.applicationContext.Event;

import  org.springframework.beans.BeansException;
import  org.springframework.context.ApplicationContext;
import  org.springframework.context.ApplicationContextAware;

public   class  Publisher  implements  ApplicationContextAware  ... {
    private ApplicationContext ctx;
    public void setApplicationContext(ApplicationContext context)
            throws BeansException ...{
        
        this.ctx=context;
    }
    
    public void publish(String message)...{
        ctx.publishEvent(new MessageEvent(this,message));
    }

}

 

配置文件:

 

<? xml version="1.0" encoding="UTF-8" ?>
< beans
     xmlns ="http://www.springframework.org/schema/beans"
    xmlns:xsi ="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation ="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd" >


< bean  id ="publisher"  class ="ch5.applicationContext.Event.Publisher" />

< bean  id ="messageEventListener"  class ="ch5.applicationContext.Event.MessageEventListener" />


</ beans >

 

测试代码:

 

package  ch5.applicationContext.Event;

import  java.io.File;
import  java.util.Locale;

import  org.springframework.context.ApplicationContext;
import  org.springframework.context.support.FileSystemXmlApplicationContext;

public   class  TestSpring  ... {


    public static void main(String[] args) ...{
         String realpath="";
           
           //加载配置项
           realpath=System.getProperty("user.dir")+File.separator+"src"+File.separator+"ch5/applicationContext/Event"+File.separator+"applicationContext.xml";

           ApplicationContext applicationContext=new FileSystemXmlApplicationContext(realpath);
           Publisher publisher=(Publisher)applicationContext.getBean("publisher");
           publisher.publish("hello world");
           publisher.publish("hello world again");
    }

}

 

运行结果:

recieve:hello world
recieve:hello world again

实现了ApplicationEventListener的类会自动执行OnApplicationEvent方法