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。