jsp简单实现统计在线人数

通过重写HttpSessionListener接口实现

 1 //session操作类
 2 public class SessionMap {
 3    
 4      private static Map<String,HttpSession> sesMap = new HashMap<String,HttpSession>();
 5    
 6      private static final Object flag = new Object();
 7    
 8      private SessionMap(){
 9    
10      }
11    
12      private static class MapUtilsN{
13          private static SessionMap sessionMap = new SessionMap();
14      }
15        
16      public static SessionMap getInstance(){
17          return MapUtilsN.sessionMap;
18      }
19        
20      public void addMap(String sessionId,HttpSession session){
21          synchronized (flag) {
22              if(!sesMap.containsKey(sessionId)){
23                  sesMap.put(sessionId, session);
24              }
25          }
26      }
27        
28      public void removeMap(String sessionId){
29          synchronized (flag) {
30              sesMap.remove(sessionId);
31          }
32      }
33        
34      public int getSize(){
35          synchronized (flag) {
36              return sesMap.size();
37          }
38      }
39        
40      public HttpSession getSession(String key){
41          synchronized (flag) {
42              return sesMap.get(key);
43          }
44       }
45 }
46   
47   
48 //监听session创建及销毁
49 public class MySessionListner implements HttpSessionListener{
50   
51  public void sessionCreated(HttpSessionEvent arg0) {
52      SessionMap.getInstance().addMap(arg0.getSession().getId(), arg0.getSession());
53  }
54   
55  public void sessionDestroyed(HttpSessionEvent arg0) {
56      SessionMap.getInstance().removeMap(arg0.getSession().getId());
57  }
58   
59 }

//web.xml中配置监听器

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app version="2.5"
 3  xmlns="http://java.sun.com/xml/ns/javaee"
 4  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 5  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
 6  http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 7   <welcome-file-list>
 8     <welcome-file>index.jsp</welcome-file>
 9   </welcome-file-list>
10   <!-- 配置监听器 -->
11   <listener>  
12       <listener-class>  
13         practice.listner.MySessionListner  
14       </listener-class>  
15   </listener>
16    <!-- 设置session超时时间 -->
17   <session-config>
18    <session-timeout>10</session-timeout>
19   </session-config>
20 </web-app>