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session 监听

1.创建一个session容器用来存放所有的用户，不同浏览器对应不用的session，下面用单例模式来创建session容器

package com.limin.framework.util;
 
import java.util.HashMap;
 
import javax.servlet.http.HttpSession;
 
import com.limin.framework.listener.SessionListener;
import com.limin.util.Util;
/**
 * 使用单例模式
 */
public class SessionContext {
    private static SessionContext instance;  
    private HashMap<String,HttpSession> sessionMap;  
    
    private SessionContext() {  
        sessionMap = new HashMap<String,HttpSession>();  
    }  
   
    public static SessionContext getInstance() {  
        if (instance == null) {  
            instance = new SessionContext();  
        }  
        return instance;  
    }  
   
    public synchronized void AddSession(HttpSession session) {  
        if (session != null) {  
            String userId = session.getAttribute("userId").toString();
            if(Util.isNotNullorEmpty(userId)){
              sessionMap.put(userId,session);
            }
        }  
    }  
   
    public synchronized void DelSession(HttpSession session) {  
        if (session != null) {  
            String userId = session.getAttribute("userId").toString();
            if(Util.isNotNullorEmpty(userId)){
                sessionMap.remove(userId);
            }
            session.invalidate(); 
        }  
    }  
   
    public HashMap<String,HttpSession> getSessionMap() {  
        return sessionMap;  
    }  
   
    public void setMymap(HashMap<String,HttpSession> sessionMap) {  
        this.sessionMap = sessionMap;  
    }  
     
    public static synchronized void sessionHandlerByCacheMap(HttpSession session){
        try {
            String userId = session.getAttribute("userId").toString();
            HttpSession userSession=(HttpSession)SessionListener.sessionContext.getSessionMap().get(userId);
            if(userSession!=null){  
                //注销在线用户  
                userSession.invalidate();
            }
            //清除在线用户后，更新map,替换map sessionid  对应session更换成新的session 
            SessionListener.sessionContext.getSessionMap().put(userId,session);  
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }    
    } 
}

　　2. 需要实现 HttpSessionListener 接口，创建一个 SessionListener

package com.limin.framework.listener;
 
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
 
import com.limin.framework.util.SessionContext;
 
public class SessionListener implements HttpSessionListener{
    public  static SessionContext sessionContext=SessionContext.getInstance();  
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {  
        sessionContext.AddSession(httpSessionEvent.getSession());  
    }  
   
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {  
        sessionContext.DelSession(httpSessionEvent.getSession());  
    }  
}