通过重写HttpSessionListener接口实现

//session操作类  public class SessionMap {           private static Map<String,HttpSession> sesMap = new HashMap<String,HttpSession>();           private static final Object flag = new Object();           private SessionMap(){           }           private static class MapUtilsN{           private static SessionMap sessionMap = new SessionMap();       }               public static SessionMap getInstance(){           return MapUtilsN.sessionMap;       }               public void addMap(String sessionId,HttpSession session){           synchronized (flag) {               if(!sesMap.containsKey(sessionId)){                   sesMap.put(sessionId, session);               }           }       }               public void removeMap(String sessionId){           synchronized (flag) {               sesMap.remove(sessionId);           }       }               public int getSize(){           synchronized (flag) {               return sesMap.size();           }       }               public HttpSession getSession(String key){           synchronized (flag) {               return sesMap.get(key);           }        }  }        //监听session创建及销毁  public class MySessionListner implements HttpSessionListener{      public void sessionCreated(HttpSessionEvent arg0) {       SessionMap.getInstance().addMap(arg0.getSession().getId(), arg0.getSession());   }      public void sessionDestroyed(HttpSessionEvent arg0) {       SessionMap.getInstance().removeMap(arg0.getSession().getId());   }     }   

//web.xml中配置监听器  <?xml version="1.0" encoding="UTF-8"?>  <web-app version="2.5"    xmlns="http://java.sun.com/xml/ns/javaee"    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">    <welcome-file-list>      <welcome-file>index.jsp</welcome-file>    </welcome-file-list>    <!-- 配置监听器 -->    <listener>          <listener-class>            practice.listner.MySessionListner          </listener-class>      </listener>     <!-- 设置session超时时间 -->    <session-config>     <session-timeout>10</session-timeout>    </session-config>  </web-app>