Servlet---Listener

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package com.an.tomcatservlet;   import javax.servlet.ServletContextAttributeEvent; import javax.servlet.ServletContextAttributeListener; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import javax.servlet.ServletRequest; import javax.servlet.ServletRequestAttributeEvent; import javax.servlet.ServletRequestAttributeListener; import javax.servlet.ServletRequestEvent; import javax.servlet.ServletRequestListener; import javax.servlet.http.HttpSessionActivationListener; import javax.servlet.http.HttpSessionAttributeListener; import javax.servlet.http.HttpSessionBindingEvent; import javax.servlet.http.HttpSessionBindingListener; import javax.servlet.http.HttpSessionEvent; import javax.servlet.http.HttpSessionListener;   /**  * @author apy  * @description  * @date 2021/10/21 17:29  */ public class MyListener implements ServletRequestListener         ,ServletRequestAttributeListener         ,ServletContextListener         ,ServletContextAttributeListener         ,HttpSessionListener         ,HttpSessionBindingListener         ,HttpSessionActivationListener         ,HttpSessionAttributeListener{       public void requestInitialized(ServletRequestEvent sre) {         ServletRequest servletRequest = sre.getServletRequest();         // do something...     }       public void requestDestroyed(ServletRequestEvent sre) {       }       public void attributeAdded(ServletRequestAttributeEvent srae) {       }       public void attributeRemoved(ServletRequestAttributeEvent srae) {       }       public void attributeReplaced(ServletRequestAttributeEvent srae) {       }       public void contextInitialized(ServletContextEvent sce) {       }       public void contextDestroyed(ServletContextEvent sce) {       }       public void attributeAdded(ServletContextAttributeEvent event) {       }       public void attributeRemoved(ServletContextAttributeEvent event) {       }       public void attributeReplaced(ServletContextAttributeEvent event) {       }       public void sessionCreated(HttpSessionEvent se) {       }       public void sessionDestroyed(HttpSessionEvent se) {       }       public void valueBound(HttpSessionBindingEvent event) {       }       public void valueUnbound(HttpSessionBindingEvent event) {       }       /**      * 【servlet Listener】      *      why？      *          解决 共享对象 内容发生变化 时， 在发生前、发生后 做处理；      *      *          Servlet2.3 提供了 对 ServletContext、HttpSession对象的变化的 监听器；      *          Servlet2.4 增加了 对 ServletRequest对象的变化的 监听器；      *      *      what？      *          ServletContext监听器：监听 ServletContext对象，可以 使 web应用 得知 web组件的 加载、卸载情况等；      *              ServletContextListener      *              ServletContextAttributeListener      *      *              ServletContextEvent      *              ServletContextAttributeEvent      *      *          HttpSession监听器：监听 HttpSession对象变化，可以 使 web应用 了解 会话期间的状态 并 做出响应；      *              HttpSessionListener      *              HttpSessionActivationListener  实现数据 内存->磁盘，磁盘->内存；      *      *              HttpSessionEvent      *      *      *              HttpSessionAttributeListener      *              HttpSessionBindingListener      *      *              HttpSessionBindingEvent      *      *      *          ServletRequest监听器：监听 ServletRequest对象变化，可以 使 web应用 控制web请求的生命周期；      *              ServletRequestListener      *              ServletRequestAttributeListener      *      *              ServletRequestEvent      *              ServletRequestAttributeEvent      *      *      How？      *          创建普通Java类，实现 对应的Listener,重写相应的方法；      *          在web.xml中配置相应的 Listener；      */ }