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(ApplicationContextapplicationContext)和发布方法publish(Objectobj)
·定义时间监听类EventListener，实现ApplicationListener接口，实现方法onApplicationEvent(ApplicationEventevent).
Java代码
importorg.springframework.context.ApplicationEvent;
/**
*定义事件信息
*@authornew
*
*/
publicclassMessageEventextendsApplicationEvent{
privateStringmessage;
publicvoidsetMessage(Stringmessage){
this.message=message;
}
publicStringgetMessage(){
returnmessage;
}
publicMessageEvent(Objectsource,Stringmessage){
super(source);
this.message=message;
//TODOAuto-generatedconstructorstub
}
privatestaticfinallongserialVersionUID=1L;
}
java代码
importorg.springframework.beans.BeansException;
importorg.springframework.context.ApplicationContext;
importorg.springframework.context.ApplicationContextAware;
importorg.springframework.context.support.FileSystemXMLApplicationContext;
publicclassPublisherimplementsApplicationContextAware{
privateApplicationContextcontext;
@Override
publicvoidsetApplicationContext(ApplicationContextarg0)
throwsBeansException{
//TODOAuto-generatedmethodstub
this.context=arg0;
}
publicvoidpublish(Stringmessage){
context.publishEvent(newMessageEvent(this,message));
}
publicstaticvoidmain(String[]args){
ApplicationContextctx=newFileSystemXmlApplicationContext("src/applicationContext.xml");
Publisherpub=(Publisher)ctx.getBean("publisher");
pub.publish("HelloWorld!");
pub.publish("Thequickbrownfoxjumpedoverthelazydog");
}
}
java代码
importorg.springframework.context.ApplicationEvent;
importorg.springframework.context.ApplicationListener;
publicclassMessageEventListenerimplementsApplicationListener{
@Override
publicvoidonApplicationEvent(ApplicationEventevent){
//TODOAuto-generatedmethodstub
if(eventinstanceofMessageEvent){
MessageEventmsEvent=(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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