jsp简单实现统计在线人数

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>