//事件涉及的三个组件:事件源、事件对象、事件监听器
//一个总的事件监听器接口，所有不同分类的事件监听器都继承这个接口
public interface EventListener {
}
//例如 ServletContextListener 这个ServletContext监听器 他有两个方法，一个是初始化方法，另一个是销毁的方法。在web.xml中配置了listener，那么容器在启动时就会扫描web.xml的listener的配置，自动调用contextInitialized 方法，在容器重启时，他会先调用contextDestroyed销毁的方法，在调用contextInitialized 创建的方法。在容器关闭时，会调用contextDestroyed方法。但我刚启动完容器，立刻关闭，是不会调用到contextDestroyed方法的。我想他这里应该有设置时间的吧。
public interface ServletContextListener extends EventListener {
/**
** Notification that the web application initialization
** process is starting.
** All ServletContextListeners are notified of context
** initialization before any filter or servlet in the web
** application is initialized.
*/
public void contextInitialized ( ServletContextEvent sce ); //接受的参数是ServletContextEvent 事件源
/** ** Notification that the servlet context is about to be shut down. ** All servlets and filters have been destroy()ed before any ** ServletContextListeners are notified of context ** destruction. */
public void contextDestroyed ( ServletContextEvent sce ); }
//每一个事件对象都有一个总的事件对象类，下面这个就是了。
public class EventObject implements java.io.Serializable {
private static final long serialVersionUID = 5516075349620653480L;
/**
* The object on which the Event initially occurred.
*/
protected transient Object source;
/**
* Constructs a prototypical Event.
*
* @param source The object on which the Event initially occurred.
* @exception IllegalArgumentException if source is null.
*/
public EventObject(Object source) {
if (source == null)
throw new IllegalArgumentException("null source");
//在这里封装一个事件源
this.source = source;
}
/**
* The object on which the Event initially occurred.
*
* @return The object on which the Event initially occurred.
*/
public Object getSource() {
return source; //得到事件源
}
/**
* Returns a String representation of this EventObject.
*
* @return A a String representation of this EventObject.
*/
public String toString() {
return getClass().getName() + "[source=" + source + "]";
}
}
public class ServletContextEvent extends java.util.EventObject {
/** Construct a ServletContextEvent from the given context.
*
* @param source - the ServletContext that is sending the event.
*/
public ServletContextEvent(ServletContext source) {
super(source);
}
/**
* Return the ServletContext that changed.
*
* @return the ServletContext that sent the event.
*/
public ServletContext getServletContext () {
return (ServletContext) super.getSource();//返回一个真正的事件源
}
}
这就是tomcat的事件监听设计模型。