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。