【JavaEE企业应用实战学习记录】sessionListener

 package sanglp.servlet;

 import javax.servlet.ServletContext;
 import javax.servlet.annotation.WebListener;
 import javax.servlet.http.HttpSession;
 import javax.servlet.http.HttpSessionEvent;
 import java.util.Hashtable;
 import java.util.Map;

 /**
  * Created by Administrator on 2016/10/6.
  */
 @WebListener
 public class HttpSessionListener implements javax.servlet.http.HttpSessionListener {

     //当用户与服务之间开始session时触发该方法
     @Override
     public void sessionCreated(HttpSessionEvent httpSessionEvent) {
         HttpSession session=httpSessionEvent.getSession();
         ServletContext application=session.getServletContext();
         //获取sessionId
         String sessionId=session.getId();
         //如果是一次新的会话
         if(session.isNew()){
             String user=(String)session.getAttribute("user");
             //未登陆用户当游客处理
             user=(user==null)?"游客":user;
             Map<String,String> online=(Map<String, String>) application.getAttribute("online");
             if(online==null){
                 online=new Hashtable<String,String>();
                 //将用户在线信息放入Map中
                 online.put(sessionId,user);
                 application.setAttribute("online",online);
             }
         }
     }

     //当用户与服务器之间session断开时触发该方法
     @Override
     public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
     HttpSession session=httpSessionEvent.getSession();
         ServletContext application=session.getServletContext();
         String sessionId=session.getId();
         Map<String,String> online=(Map<String,String>)application.getAttribute("online");
         if(online!=null){
             //删除该用户的在线信息
             online.remove(sessionId);
         }
         application.setAttribute("online",online);
     }
 }