Spring中事件处理的小技巧

Spring中提供一些Aware相关的接口，BeanFactoryAware、 ApplicationContextAware、ResourceLoaderAware、ServletContextAware等等，其中最常用到的是ApplicationContextAware。实现ApplicationContextAware的Bean，在Bean被初始后，将会被注入 ApplicationContext的实例。ApplicationContextAware提供了publishEvent()方法，实现Observer(观察者)设计模式的事件传播机，提供了针对Bean的事件传播功能。通过Application.publishEvent方法，我们可以将事件通知系统内所有的ApplicationListener。

Spring事件处理一般过程：

·定义Event类，继承org.springframework.context.ApplicationEvent.

·编写发布事件类Publisher，实现org.springframework.context.ApplicationContextAware接口.

·覆盖方法setApplicationContext(ApplicationContext applicationContext)和发布方法publish(Object obj)

·定义时间监听类EventListener，实现ApplicationListener接口，实现方法onApplicationEvent(ApplicationEvent event).

java 代码

import org.springframework.context.ApplicationEvent; /** * 定义事件信息 * @author new * */ public class MessageEvent extends ApplicationEvent { private String message; public void setMessage(String message){ this.message = message; } public String getMessage(){ return message; } public MessageEvent(Object source, String message) { super(source); this.message = message; // TODO Auto-generated constructor stub } private static final long serialVersionUID = 1L; }

java 代码

import org.springframework.beans.BeansException; import org.springframework.context.ApplicationContext; import org.springframework.context.ApplicationContextAware; import org.springframework.context.support.FileSystemXmlApplicationContext; public class Publisher implements ApplicationContextAware { private ApplicationContext context; @Override public void setApplicationContext(ApplicationContext arg0) throws BeansException { // TODO Auto-generated method stub this.context = arg0; } public void publish(String message){ context.publishEvent(new MessageEvent(this,message)); } public static void main(String[] args) { ApplicationContext ctx = new FileSystemXmlApplicationContext("src/applicationContext.xml"); Publisher pub = (Publisher) ctx.getBean("publisher"); pub.publish("Hello World!"); pub.publish("The quick brown fox jumped over the lazy dog"); } }

java 代码

import org.springframework.context.ApplicationEvent; import org.springframework.context.ApplicationListener; public class MessageEventListener implements ApplicationListener { @Override public void onApplicationEvent(ApplicationEvent event) { // TODO Auto-generated method stub if(event instanceof MessageEvent){ MessageEvent msEvent = (MessageEvent)event; System.out.println("Received: " + msEvent.getMessage()); } } }

在运行期，ApplicationContext会自动在当前的所有Bean中寻找ApplicationListener接口的实现，并将其作为事件接收对象。当Application.publishEvent方法调用时，所有的ApplicationListener接口实现都会被激发，每个ApplicationListener可根据事件的类型判断是否是自己需要处理的事件，如上面的ActionListener只处理ActionEvent事件。