13.JavaWeb基础 监听器

   监听器俗称监听Servlet。主要的功能是负责监听Web的各种操作，当相关的事件触发

之后将产生事件，并对此事件进行处理。在Web中可以对request、session、application

属性进行监听操作。

一.对application监听

ApplicationListener：

package com.zyy.listener;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;public class ApplicationListener implements ServletContextListener {public void contextDestroyed(ServletContextEvent event) {System.out.println("*************************Application销毁："+ event.getServletContext().getContextPath());}public void contextInitialized(ServletContextEvent event) {System.out.println("***************************Application初始化："+ event.getServletContext().getContextPath());}}

web.xml：

  <listener>    <listener-class>com.zyy.listener.ApplicationListener</listener-class>    </listener>

ApplicationAttributeListener：

package com.zyy.listener;import javax.servlet.ServletContextAttributeEvent;import javax.servlet.ServletContextAttributeListener;public class ApplicationAttributeListener implementsServletContextAttributeListener {public void attributeAdded(ServletContextAttributeEvent event) {System.out.println("Application增加属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}public void attributeRemoved(ServletContextAttributeEvent event) {System.out.println("Application删除属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}public void attributeReplaced(ServletContextAttributeEvent event) {System.out.println("Application更新属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}}

web.xml：

  <listener>    <listener-class>com.zyy.listener.ApplicationAttributeListener</listener-class>    </listener>

测试代码：

<%this.getServletContext().setAttribute("CaMnter", "Save you from anything 07") ;        this.getServletContext().setAttribute("CaMnter", "Save you from anything 07 forever") ;this.getServletContext().removeAttribute("CaMnter") ;%>

刷新好多次页面得到如下：

二.对session监听

SessionListener：

package com.zyy.listener;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;public class SessionListener implements HttpSessionListener {public void sessionCreated(HttpSessionEvent event) {System.out.println("***** Session创建  id：" + event.getSession().getId());}public void sessionDestroyed(HttpSessionEvent event) {System.out.println("***** Session摧毁  id：" + event.getSession().getId());}}

web.xml：

  <listener>    <listener-class>com.zyy.listener.SessionListener</listener-class>    </listener>

测试代码：

<%session.invalidate();%>

刷新好多次页面得到如下：

SessionAttributeListener：

package com.zyy.listener;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;public class SessionAttributeListener implements HttpSessionAttributeListener {public void attributeAdded(HttpSessionBindingEvent event) {System.out.println("Session增加属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}public void attributeRemoved(HttpSessionBindingEvent event) {System.out.println("Session删除属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}public void attributeReplaced(HttpSessionBindingEvent event) {System.out.println("Session更新属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}}

web.xml：

  <listener>    <listener-class>com.zyy.listener.SessionAttributeListener</listener-class>    </listener>

测试代码：

<%session.setAttribute("CaMnter", "Save you from anything 07") ;session.removeAttribute("CaMnter");%>

刷新好多次页面得到如下：

三.对request监听

RequestListener：

package com.zyy.listener;import javax.servlet.ServletRequestEvent;import javax.servlet.ServletRequestListener;public class RequestListener implements ServletRequestListener {public void requestDestroyed(ServletRequestEvent event) {System.out.println("Request 销毁："+ event.getServletRequest().getRemoteAddr()+ event.getServletContext().getContextPath());}public void requestInitialized(ServletRequestEvent event) {System.out.println("Request 初始化："+ event.getServletRequest().getRemoteAddr()+ event.getServletContext().getContextPath());}}

web.xml：

  <listener>    <listener-class>com.zyy.listener.RequestListener</listener-class>    </listener>

这个不需要测试代码，发布项目后，连接到即可。比如（http://127.0.0.1:8080/Listener）。

然后多次刷新后得到：

RequestAttributeListener：

package com.zyy.listener;import javax.servlet.ServletRequestAttributeEvent;import javax.servlet.ServletRequestAttributeListener;public class RequestAttributeListener implementsServletRequestAttributeListener {public void attributeAdded(ServletRequestAttributeEvent event) {System.out.println("Request增加属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}public void attributeRemoved(ServletRequestAttributeEvent event) {System.out.println("Request删除属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}public void attributeReplaced(ServletRequestAttributeEvent event) {System.out.println("Request更新属性：" + " name = " + event.getName()+ " ,value = " + event.getValue());}}

web.xml：

  <listener>    <listener-class>com.zyy.listener.RequestAttributeListener</listener-class>    </listener>

测试代码：

<%request.setAttribute("CaMnter", "Save you from anything 07") ;request.setAttribute("CaMnter", "Save you from anything 07 forever") ;request.removeAttribute("CaMnter") ;%>