异地防止重复登录

小灰灰 2022-06-01 12:43 182阅读 0赞

# 异地防止重复登录 #

**将用户的登录信息保存在Application内置作用域中，利用session监听每一个登录用户的登录情况。**  
*用户登录成功后将用户的登录信息已键值对的形式保存在Application中，由于Application是保存在服务器端，当用户在异地登录时，将登录信息与Application中的键值对进行比较如果相同则登录失败。*

**如图所示为目录结构：**  
![这里写图片描述][SouthEast]  
**核心代码片段：**

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            //获取表单中的username和password
            String username = req.getParameter("username");
            String password = req.getParameter("password");
            HttpSession session = req.getSession();//初始化session
            UserBean user = null;
            try {
                System.out.println(username + "ceshi " + password);
                user = userService.login(username, password);//
    
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 
            if (user != null) {
                //初始化Context变量
                ServletContext application = session.getServletContext();
                //初始化map集合
                Map<String, String> loginMap = (Map<String, String>) application.getAttribute("loginMap");
    
                if (loginMap == null) {
                    loginMap = new HashMap<>();
                }
                //
                for (String key : loginMap.keySet()) {
                    if (user.getUsername().equals(key)) {
                        if (session.getId().equals(loginMap.get(key))) {
                            System.out.println(username + "在同一地点多次登录！");
                        } else {
                            System.out.println(username + "异地登录被拒绝！");
                            session.setAttribute("tip", "该用户已经异地登录！");
                            req.getRequestDispatcher("index.jsp").forward(req, resp);
                        }
                    }
                }
                loginMap.put(user.getUsername(), session.getId());
                application.setAttribute("loginMap", loginMap);
                session.setAttribute("username", user.getUsername());
                System.out.println("登录成功！");
                resp.sendRedirect("index.jsp");
            } 
            else {
                // 登录失败
                System.out.println("user is null");
                session.setAttribute("tip", "登录失败！");
                req.getRequestDispatcher("index.jsp").forward(req, resp);
            }
        }

session监听：

public void sessionDestroyed(HttpSessionEvent event) {
            //在session销毁的时候 把loginMap中保存的键值对清除
            String username = event.getSession().getAttribute("username").toString();
            if(username!=null){
                Map<String, String> loginMap = (Map<String, String>)event.getSession().getServletContext().getAttribute("loginMap");
                loginMap.remove(username);
                event.getSession().getServletContext().setAttribute("loginMap",loginMap);
                System.out.println(username+"用户注销！");
            }
        }

效果如图所示：  
![这里写图片描述][SouthEast 1]  
异地登录

## ![这里写图片描述][SouthEast 2] ##

下载链接  
[https://github.com/Gwisdomm/CheckLogin][https_github.com_Gwisdomm_CheckLogin])

[SouthEast]: /images/20220601/36a201de272f4427bc3c3b2119123fc8.png
[SouthEast 1]: /images/20220601/90cd8a204edf445e9867aa9637ce0a36.png
[SouthEast 2]: /images/20220601/29ce051054134335a37b9c6cd434d39e.png
[https_github.com_Gwisdomm_CheckLogin]: https://github.com/Gwisdomm/CheckLogin