• Spring中事件处理的小技巧
    时间:2008-11-18   作者:佚名   出处:互联网

    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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