请问如何实现jsp的在线人数统计

Question

http://www.javaresearch.org/article/showarticle.jsp?column=106&thread=406

Answer 1

package net.htjs.onlineusers;import java.util.*;
import javax.servlet.*; 
import javax.servlet.http.*; public class OnLineUsers implements HttpSessionListener 
{     private static Hashtable hmUserList = new Hashtable();
private static boolean active = false;     public synchronized int getUserCount()
    {
        return hmUserList.size();
    }
   
    public synchronized void addUser(String sessionID,String userName)
    {
    //System.out.println("addUser");
        hmUserList.put(sessionID,userName);
    }
   
    public synchronized boolean existUser(String userName)
    {
    //System.out.println("existUser");
        Set set = hmUserList.keySet();
        Iterator iterator = set.iterator();
        while(iterator.hasNext())
        {
        String user = (String)hmUserList.get(iterator.next());
            if(userName.equals(user))
            {
                return true;
            }
        }
       
        return false;
    }    public synchronized void deleteUser(String sessionID) 
    {
    //System.out.println("deleteUser:"+sessionID);
hmUserList.remove(sessionID);
    }    public synchronized Iterator getOnLineUser()
    {
        Set set = hmUserList.keySet();
        return set.iterator();
    }

public void sessionCreated(HttpSessionEvent se) 
{ 
active = true;
}  public void sessionDestroyed(HttpSessionEvent se) 
{ 
deleteUser(se.getSession().getId());
active = false;
}  public static boolean getActiveSession()
{ 
return active; 
} 
} web.xml中加入
  <listener>
    <listener-class>net.htjs.onlineusers.OnLineUsers</listener-class>
  </listener>

Answer 2

http://www.javaresearch.org/article/showarticle.jsp?column=106&thread=406