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Spring中事件处理小技巧

  【IT168 技术文档】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。

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