同一个账号，同一时间只能允许他登录一次

package com.beyondlife.listener; import java.util.HashMap; import java.util.Map; import javax.servlet.ServletContext; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import javax.servlet.http.HttpSession; import javax.servlet.http.HttpSessionAttributeListener; import javax.servlet.http.HttpSessionBindingEvent; import javax.servlet.http.HttpSessionEvent; import javax.servlet.http.HttpSessionListener; import com.beyondlife.vo.UList; import com.beyondlife.vo.User; public class UserListener implements ServletContextListener, HttpSessionListener,HttpSessionAttributeListener{ ServletContext application = null; //服务器关闭时清空内容 public void contextDestroyed(ServletContextEvent event) { Map ulist = (Map)event.getServletContext().getAttribute("ulist"); if(ulist != null){ ulist.clear(); } } public void contextInitialized(ServletContextEvent event) { //初始化用户列表 Map ulist = new HashMap(); application = event.getServletContext(); application.setAttribute("ulist", ulist); } public void sessionCreated(HttpSessionEvent event) { } //把用户过期或者注销把用户信息删除 public void sessionDestroyed(HttpSessionEvent event) { HttpSession session = event.getSession(); User user = (User)session.getAttribute("user"); if(user != null){ System.out.println(user.getSerial()); Map ulist = (Map)application.getAttribute("ulist"); UList ul = (UList)ulist.get(user.getUid()); if(ul != null && ul.getSerial().equals(user.getSerial())){ ulist.remove(user.getUid()); } } } public void attributeAdded(HttpSessionBindingEvent event) { Object obj = event.getValue(); if(obj.getClass().getName().equals("com.beyondlife.vo.User")){ User user = (User)obj; //建立用户列表实体 UList ul = new UList(); ul.setSerial(user.getSerial()); ul.setUid(user.getUid()); ul.setName(user.getName()); //如果用户已经登陆他的信息将会被map映射替代，因为KEY是 唯一的UID Map ulist = (Map)application.getAttribute("ulist"); ulist.put(user.getUid(), ul); } } public void attributeRemoved(HttpSessionBindingEvent event) { Object obj = event.getValue(); if(obj.getClass().getName().equals("com.beyondlife.vo.User")){ User user = (User)obj; //该用户的信息消除 Map ulist = (Map)application.getAttribute("ulist"); ulist.remove(user.getUid()); } } //用户重新登陆 public void attributeReplaced(HttpSessionBindingEvent event) { Object obj = event.getValue(); if(obj.getClass().getName().equals("com.beyondlife.vo.User")){ User user = (User)event.getSession().getAttribute("user"); //建立用户列表实体 UList ul = new UList(); ul.setSerial(user.getSerial()); ul.setUid(user.getUid()); ul.setName(user.getName()); //用户原来的信息将会被map映射替代，因为KEY是唯一的UID Map ulist = (Map)application.getAttribute("ulist"); ulist.put(user.getUid(), ul); } } }