常用应用场景:单点登录、统计在线人数
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 session public void sessionCreated(HttpSessionEvent se) { HttpSession session = se.getSession(); log.info("新创建一个session, ID为: " + session.getId()); } // 销毁 session public void sessionDestroyed(HttpSessionEvent se) { HttpSession session = se.getSession(); log.info("销毁一个session, ID为: " + session.getId()); } // 加载 context public void contextInitialized(ServletContextEvent sce) { ServletContext servletContext = sce.getServletContext(); log.info("即将启动" + servletContext.getContextPath()); } // 卸载 context public void contextDestroyed(ServletContextEvent sce) { ServletContext servletContext = sce.getServletContext(); log.info("即将关闭" + servletContext.getContextPath()); } // 创建 request public 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 request public 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"); } @Override public 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; } @Override public 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; } @Override public 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 map ApplicationConstants.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(); } } } } }