Map<String, HttpSession> map=(Map<String, HttpSession>) sc.getAttribute("users");//保存所有登录有关的map对象

package com.tfy.heima.listener;


import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;


import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;


import com.tfy.heima.domain.User;


public class OnlineUserListener implements HttpSessionAttributeListener {
//Map<String,HttpSession>
public void attributeAdded(HttpSessionBindingEvent se) {
      HttpSession session=se.getSession();
      Object obj=session.getAttribute("user");
      if(obj!=null && obj instanceof User){
     User user=(User)obj;
     ServletContext sc=session.getServletContext();
     Map<String, HttpSession> map=(Map<String, HttpSession>) sc.getAttribute("users");//保存所有登录有关的map对象
     if(map==null){
     map=Collections.synchronizedMap(new HashMap<String, HttpSession>());
     sc.setAttribute("users", map);
     }
     map.put(user.getUsername(), session);
      }
}


public void attributeRemoved(HttpSessionBindingEvent se) {


}


public void attributeReplaced(HttpSessionBindingEvent se) {


}


}