tomcat的事件监听

//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。