监听器

1.ServletContextListener   servletContext监听器

它包含两个方法

(1) public void contextInitialized ( ServletContextEvent sce ); //监听到servletContext创建时调用

(2) public void contextDestroyed ( ServletContextEvent sce );//监听到servletContext销毁时调用

要实现对创建或销毁事件进行监听，只需要实现相应的方法，并在web.xml中配置即可

2.ServletContextAttributeListener servletContext属性监听器

（1）public void attributeAdded(ServletContextAttributeEvent scab); //增加属性

（2）public void attributeRemoved(ServletContextAttributeEvent scab);  //移除属性

（3）public void attributeReplaced(ServletContextAttributeEvent scab);  //更改属性

3.ServletRequestListener

  (1)public void requestDestroyed ( ServletRequestEvent sre );

  (2) public void requestInitialized ( ServletRequestEvent sre );

4.ServletRequestAttributeListener

    public void attributeAdded(ServletRequestAttributeEvent srae);

    public void attributeRemoved(ServletRequestAttributeEvent srae);

    public void attributeReplaced(ServletRequestAttributeEvent srae);