Servlet学习笔记（九）：监听器Listener详解

一、简介

（一）概述

1、Listener 用于监听 java web程序中的事件，例如创建、修改、删除Session、request、context等，并触发响应的事件。

2、 Listener 对应观察者模式，事件发生的时候会自动触发该事件对应的Listeer。 Listener 主要用于对 Session、request、context 进行监控。servlet2.5 规范中共有 8 种Listener  。

（二）实现

1、不同功能的Listener 需要实现不同的 Listener  接口，一个Listener也可以实现多个接口，这样就可以多种功能的监听器一起工作。

2、8种监听器可以分为三类：

1）监听 Session、request、context 的创建于销毁，分别为  

HttpSessionLister、ServletContextListener、ServletRequestListener

2）监听对象属性变化，分别为：

HttpSessionAttributeLister、ServletContextAttributeListener、ServletRequestAttributeListener 

3）监听Session 内的对象，分别为HttpSessionBindingListener 和 HttpSessionActivationListener。与上面六类不同，这两类 Listener 监听的是Session 内的对象，而非 Session 本身，不需要在 web.xml中配置。

2、实现web.xml的Listener配置。

1）<listener>标签与 <listener-class>

2）<listener>一般配置在 <servlet>便签的前面。

package servlet.listener;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;/** *  * MyListener.java * * @title Context监听器 * @description * @author SAM-SHO  * @Date 2014-9-25 */public class MyListener implements ServletContextListener {public void contextDestroyed(ServletContextEvent sce) {}public void contextInitialized(ServletContextEvent sce) {}}

<!--监听器 --><listener><listener-class>servlet.listener.MyListener</listener-class></listener>

二、八种类型监听器

（一）监听 Session、request、context 的创建于销毁。

 HttpSessionLister、ServletContextListener、ServletRequestListener

1、三种监听器的触发时机及使用：

2、实例：实现监听对象的创建与销毁

package servlet.listener;import javax.servlet.ServletContext;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import javax.servlet.ServletRequestEvent;import javax.servlet.ServletRequestListener;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;/** *  * ListenerTest.java *  * @title 监听对象的创建与销毁 * @description * @author SAM-SHO * @Date 2014-12-10 */public class ListenerTest implements HttpSessionListener, ServletContextListener, ServletRequestListener {Log log = LogFactory.getLog(getClass());// 创建 sessionpublic void sessionCreated(HttpSessionEvent se) {HttpSession session = se.getSession();log.info("新创建一个session, ID为: " + session.getId());}// 销毁 sessionpublic void sessionDestroyed(HttpSessionEvent se) {HttpSession session = se.getSession();log.info("销毁一个session, ID为: " + session.getId());}// 加载 contextpublic void contextInitialized(ServletContextEvent sce) {ServletContext servletContext = sce.getServletContext();log.info("即将启动" + servletContext.getContextPath());}// 卸载 contextpublic void contextDestroyed(ServletContextEvent sce) {ServletContext servletContext = sce.getServletContext();log.info("即将关闭" + servletContext.getContextPath());}// 创建 requestpublic void requestInitialized(ServletRequestEvent sre) {HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();String uri = request.getRequestURI();uri = request.getQueryString() == null ? uri : (uri + "?" + request.getQueryString());request.setAttribute("dateCreated", System.currentTimeMillis());log.info("IP " + request.getRemoteAddr() + " 请求 " + uri);}// 销毁 requestpublic void requestDestroyed(ServletRequestEvent sre) {HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();long time = System.currentTimeMillis() - (Long) request.getAttribute("dateCreated");log.info(request.getRemoteAddr() + "请求处理结束, 用时" + time + "毫秒. ");}}

（二）监听对象属性变化，分别为HttpSessionAttributeLister、ServletContextAttributeListener、ServletRequestAttributeListener 

1、三种监听器的触发时机及使用：

2、实例：实现对象属性的监听

package servlet.listener;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;/** *  * SessionAttributeListenerTest.java * * @title 监听Session对象的属性 * @description * @author SAM-SHO  * @Date 2014-12-10 */public class SessionAttributeListenerTest implements HttpSessionAttributeListener {Log log = LogFactory.getLog(getClass());// 添加属性public void attributeAdded(HttpSessionBindingEvent se) {HttpSession session = se.getSession();String name = se.getName();log.info("新建session属性：" + name + ", 值为：" + se.getValue());}// 删除属性public void attributeRemoved(HttpSessionBindingEvent se) {HttpSession session = se.getSession();String name = se.getName();log.info("删除session属性：" + name + ", 值为：" + se.getValue());}// 修改属性public void attributeReplaced(HttpSessionBindingEvent se) {HttpSession session = se.getSession();String name = se.getName();Object oldValue = se.getValue();log.info("修改session属性：" + name + ", 原值：" + oldValue + ", 新值：" + session.getAttribute(name));}}

（三）监听Session 内的对象，分别为HttpSessionBindingListener 和 HttpSessionActivationListener

1、触发时机及使用：对象必须实现Listener接口，不需要在web.xml中配置

2、实例：实现对象属性的监听

package servlet.listener;import java.io.Serializable;import java.util.Date;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionActivationListener;import javax.servlet.http.HttpSessionBindingEvent;import javax.servlet.http.HttpSessionBindingListener;import javax.servlet.http.HttpSessionEvent;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;/** *  * PersonInfo.java * * @title 同时实现多个接口 * 被串行化，需要实现Serializable接口 * @description * @author SAM-SHO  * @Date 2014-12-10 */public class PersonInfo implements HttpSessionActivationListener, HttpSessionBindingListener, Serializable {private static final long serialVersionUID = -4780592776386225973L;Log log = LogFactory.getLog(getClass());private String name;private Date dateCreated;// 从硬盘加载后public void sessionDidActivate(HttpSessionEvent se) {HttpSession session = se.getSession();log.info(this + "已经成功从硬盘中加载。sessionId: " + session.getId());}// 即将被钝化到硬盘时public void sessionWillPassivate(HttpSessionEvent se) {HttpSession session = se.getSession();log.info(this + "即将保存到硬盘。sessionId: " + session.getId());}// 被放进session前public void valueBound(HttpSessionBindingEvent event) {HttpSession session = event.getSession();String name = event.getName();log.info(this + "被绑定到session \"" + session.getId() + "\"的" + name + "属性上");// 记录放到session中的时间this.setDateCreated(new Date());}// 从session中移除后public void valueUnbound(HttpSessionBindingEvent event) {HttpSession session = event.getSession();String name = event.getName();log.info(this + "被从session \"" + session.getId() + "\"的" + name + "属性上移除");}@Overridepublic String toString() {return "PersonInfo(" + name + ")";}public String getName() {return name;}public void setName(String name) {this.name = name;}public Date getDateCreated() {return dateCreated;}public void setDateCreated(Date dateCreated) {this.dateCreated = dateCreated;}}

三、Listener 实例

（一）单态登录：一个账号只能在一台机器上登录。

1、Listener 的代码：

package servlet.listener.singleton;import java.util.HashMap;import java.util.Map;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;/** *  * LoginSessionListener.java * * @title 实现单态登录的监听器 * @description * @author SAM-SHO  * @Date 2014-12-10 */public class LoginSessionListener implements HttpSessionAttributeListener {Log log = LogFactory.getLog(this.getClass());Map<String, HttpSession> map = new HashMap<String, HttpSession>();public void attributeAdded(HttpSessionBindingEvent event) {String name = event.getName();// 登录if (name.equals("personInfo")) {PersonInfo personInfo = (PersonInfo) event.getValue();if (map.get(personInfo.getAccount()) != null) {// map 中有记录，表明该帐号在其他机器上登录过，将以前的登录失效HttpSession session = map.get(personInfo.getAccount());PersonInfo oldPersonInfo = (PersonInfo) session.getAttribute("personInfo");//map已经存在的旧的信息log.info("帐号" + oldPersonInfo.getAccount() + "在" + oldPersonInfo.getIp() + "已经登录，该登录将被迫下线。");session.removeAttribute("personInfo");session.setAttribute("msg", "您的帐号已经在其他机器上登录，您被迫下线。");}// 将session以用户名为索引，放入map中map.put(personInfo.getAccount(), event.getSession());log.info("帐号" + personInfo.getAccount() + "在" + personInfo.getIp() + "登录。");}}public void attributeRemoved(HttpSessionBindingEvent event) {String name = event.getName();// 注销if (name.equals("personInfo")) {// 将该session从map中移除PersonInfo personInfo = (PersonInfo) event.getValue();map.remove(personInfo.getAccount());log.info("帐号" + personInfo.getAccount() + "注销。");}}public void attributeReplaced(HttpSessionBindingEvent event) {String name = event.getName();// 没有注销的情况下，用另一个帐号登录if (name.equals("personInfo")) {// 移除旧的的登录信息PersonInfo oldPersonInfo = (PersonInfo) event.getValue();map.remove(oldPersonInfo.getAccount());// 新的登录信息PersonInfo personInfo = (PersonInfo) event.getSession().getAttribute("personInfo");// 也要检查新登录的帐号是否在别的机器上登录过if (map.get(personInfo.getAccount()) != null) {// map 中有记录，表明该帐号在其他机器上登录过，将以前的登录失效HttpSession session = map.get(personInfo.getAccount());session.removeAttribute("personInfo");session.setAttribute("msg", "您的帐号已经在其他机器上登录，您被迫下线。");}map.put("personInfo", event.getSession());}}}

package servlet.listener.singleton;import java.io.Serializable;import java.util.Date;/** *  * PersonInfo.java * * @title  * @description * @author SAM-SHO  * @Date 2014-12-10 */public class PersonInfo implements Serializable {private static final long serialVersionUID = 4063725584941336123L;// 帐号private String account;// 登录IP地址private String ip;// 登录时间private Date loginDate;public String getAccount() {return account;}public void setAccount(String account) {this.account = account;}public String getIp() {return ip;}public void setIp(String ip) {this.ip = ip;}public Date getLoginDate() {return loginDate;}public void setLoginDate(Date loginDate) {this.loginDate = loginDate;}@Overridepublic int hashCode() {final int prime = 31;int result = 1;result = prime * result + ((account == null) ? 0 : account.hashCode());result = prime * result + ((ip == null) ? 0 : ip.hashCode());return result;}@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;PersonInfo other = (PersonInfo) obj;if (account == null) {if (other.account != null)return false;} else if (!account.equals(other.account))return false;if (ip == null) {if (other.ip != null)return false;} else if (!ip.equals(other.ip))return false;return true;}}

<!-- 单态登录监听器 --><listener><listener-class>servlet.listener.singleton.LoginSessionListener</listener-class></listener>

（二）显示在线人数：会需要3个监听器。

1、ContextListener：获取服务启动的时间等。

2、RequestListener：获取客户端的IP、访问地址，访问次数等。

3、SessionListener：需要监听 Session 的创建与属性变化。

4、代码如下：

package com.helloweenvsfei.listener;import java.util.Date;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import com.helloweenvsfei.util.ApplicationConstants;public class MyContextListener implements ServletContextListener {public void contextInitialized(ServletContextEvent event) {// 启动时，记录服务器启动时间ApplicationConstants.START_DATE = new Date();}public void contextDestroyed(ServletContextEvent event) {// 关闭时，将结果清除。也可以将结果保存到硬盘上。ApplicationConstants.START_DATE = null;ApplicationConstants.MAX_ONLINE_COUNT_DATE = null;}}

package com.helloweenvsfei.listener;import javax.servlet.ServletRequestEvent;import javax.servlet.ServletRequestListener;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpSession;public class MyRequestListener implements ServletRequestListener {public void requestDestroyed(ServletRequestEvent event) {}public void requestInitialized(ServletRequestEvent event) {HttpServletRequest request = (HttpServletRequest) event.getServletRequest();HttpSession session = request.getSession(true);// 记录IP地址session.setAttribute("ip", request.getRemoteAddr());// 记录访问次数，只记录访问 .html, .do, .jsp, .action 的累计次数String uri = request.getRequestURI();String[] suffix = { ".html", ".do", ".jsp", ".action" };for (int i=0; i<suffix.length; i++) {if (uri.endsWith(suffix[i])) {break;}if(i == suffix.length-1)return;}Integer activeTimes = (Integer) session.getAttribute("activeTimes");if (activeTimes == null) {activeTimes = 0;}session.setAttribute("activeTimes", activeTimes + 1);}}

package com.helloweenvsfei.listener;import java.util.Date;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;import com.helloweenvsfei.util.ApplicationConstants;public class MySessionListener implements HttpSessionListener,HttpSessionAttributeListener {public void sessionCreated(HttpSessionEvent sessionEvent) {HttpSession session = sessionEvent.getSession();// 将 session 放入 mapApplicationConstants.SESSION_MAP.put(session.getId(), session);// 总访问人数++ApplicationConstants.TOTAL_HISTORY_COUNT++;// 如果当前在线人数超过历史记录，则更新最大在线人数，并记录时间if (ApplicationConstants.SESSION_MAP.size() > ApplicationConstants.MAX_ONLINE_COUNT) {ApplicationConstants.MAX_ONLINE_COUNT = ApplicationConstants.SESSION_MAP.size();ApplicationConstants.MAX_ONLINE_COUNT_DATE = new Date();}}public void sessionDestroyed(HttpSessionEvent sessionEvent) {HttpSession session = sessionEvent.getSession();// 将session从map中移除ApplicationConstants.SESSION_MAP.remove(session.getId());}public void attributeAdded(HttpSessionBindingEvent event) {if (event.getName().equals("personInfo")) {// 当前登录用户数++ApplicationConstants.CURRENT_LOGIN_COUNT++;HttpSession session = event.getSession();// 查找该帐号有没有在其他机器上登录for (HttpSession sess : ApplicationConstants.SESSION_MAP.values()) {// 如果该帐号已经在其他机器上登录，则以前的登录失效if (event.getValue().equals(sess.getAttribute("personInfo"))&& session.getId() != sess.getId()) {sess.invalidate();}}}}public void attributeRemoved(HttpSessionBindingEvent event) {// 注销 当前登录用户数--if (event.getName().equals("personInfo")) {ApplicationConstants.CURRENT_LOGIN_COUNT--;}}public void attributeReplaced(HttpSessionBindingEvent event) {// 重新登录if (event.getName().equals("personInfo")) {HttpSession session = event.getSession();for (HttpSession sess : ApplicationConstants.SESSION_MAP.values()) {// 如果新帐号在其他机器上登录过，则以前登录失效if (event.getValue().equals(sess.getAttribute("personInfo"))&& session.getId() != sess.getId()) {sess.invalidate();}}}}}