Servlet判断用户是否登陆过、异地登录和登出功能

朴灿烈づ我的快乐病毒、 2023-03-01 08:41 50阅读 0赞

Servlet判断用户是否登陆过和异地登录功能  
利用ServletContext+session+监听器(Listener)实现  
做login界面时当用户进行登录会有用户再次登录的情况,如果一个账户两个人同时登录会有许多不必要的麻烦,针对以上情况做出了一下代码的修改  
首先是两个简单的界面  
**login.html**

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>登录界面</title>
    </head>
    <body>
    
    <form action="login" method="post">
        用户:<input type="text" name="username"><br />
        密码:<input type="password" name="password"><br />
        <input type="submit" value="登录">
    </form>
    </body>
    </html>

**hello.html**

<!DOCTYPE html>
    <html lang="en">
    <head>
      <meta charset="UTF-8">
      <title>登录成功界面</title>
    </head>
    <body>
    <h1>欢迎您的到来,尊敬的VIP用户</h1>
    <input type="button" value="退出" onclick="location='loginOut'">
    
    </body>
    </html>

然后是用户类,get和set数据,我这里只是简单的创建了一个  
**User**

/** * @description: 用户类 **/
    public class User { 
        private String username;
        private String password;
    
        public User() { 
        }
    
        public User(String username, String password) { 
            this.username = username;
            this.password = password;
        }
    
        public String getUsername() { 
            return username;
        }
    
        public void setUsername(String username) { 
            this.username = username;
        }
    
        public String getPassword() { 
            return password;
        }
    
        public void setPassword(String password) { 
            this.password = password;
        }
    
        @Override
        public String toString() { 
            return "User{" +
                    "username='" + username + '\'' +
                    ", password='" + password + '\'' +
                    '}';
        }
    }

接下来是UserDao的操作  
**UserDao**  
在这里只写了一个查询用户名和密码是否正确的接口

public interface UserDao { 
        User loginUser(String username,String password);
    }

**UserDaoImpl**实现UserDao里的接口  
模拟了一下数据库进行查找数据的操作,可根据自己的数据库重写

public class UserDaoImpl implements UserDao{ 
        @Override
        public User loginUser(String username, String password) { 
            //假设数据库传值
            boolean flag = "111".equals(username)&&"111".equals(password);
            if (flag){ 
                return new User(username,password);
            }
            return null;
        }
    }

**LoginServlet**  
进行登录时的servlet判断

import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    import java.io.IOException;
    import java.util.HashMap;
    import java.util.Map;
    
    /** * @description: 登录servlet **/
    @WebServlet("/login")  //这个注解相当于xml里给LoginServlet添加路径
    public class LoginServlet extends HttpServlet { 
        @Override
        public void service(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException{ 
            //设置请求编码
            request.setCharacterEncoding("utf-8");
            //设置响应格式及编码
            response.setContentType("text/html;charset=utf-8");
            //获得界面传过来的参数
            String username = request.getParameter("username");
            String password = request.getParameter("password");
            //进行dao查询
            UserDao dao = new UserDaoImpl();
            User user = dao.loginUser(username,password);
            //创建上下文对象
            ServletContext sc = request.getServletContext();
            //创建session
            HttpSession session = request.getSession();
            //获得session的id
            String sessionId = session.getId();
            //获取存储用户的map<用户名,sessionId>---map里的用户名也可以换成用户对象,只要保证key值唯一
            Map<String,String> map = (Map<String, String>) sc.getAttribute("loginMap");
            if (map == null){ 
                map = new HashMap<>();
            }
            if (user != null){ 
                //迭代map,并判断是否登录过
                for (String name : map.keySet()){ 
                    System.out.println(111);
                    //user一样表示登录过
                    if (username.equals(name)){ 
                        //sessionId值一样的话,表示重复登录
                        if (sessionId.equals(map.get(name))){ 
                            System.out.println("用户重复");
                            response.getWriter().println("<h1>用户重复登录</h1>");
                            return;
                        }else{  //sessionId值不一样,表示异地登录
                            response.getWriter().println("<h1>禁止异地登录</h1>");
                            return;
                        }
                    }
                }
                //如果user没有一样的,就没有登录过将当前用户添加到map
                map.put(username,sessionId);
                sc.setAttribute("loginMap",map);
                //将当前用户添加到session
                session.setAttribute("username",username);
                response.sendRedirect("index.html");
            }else { 
                response.getWriter().println("<h1>用户名或密码错误</h1>");
            }
    
        }
    }

**LoginOutServlet**  
用户登出时,把当前sessionId值给手动消除,然后重定向到登录页面

import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    /** * @description: 用户登出 **/
    @WebServlet("/loginOut")
    public class LoginOutServlet extends HttpServlet { 
        @Override
        public void service(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException{ 
            request.getSession().invalidate();
            response.sendRedirect("hello.html");
        }
    }

**LoginListener**  
当用户登出,手动销毁了sessionId,然后监听器监听到sessionId的销毁,进行如下操作,重新添加map

import javax.servlet.ServletContext;
    import javax.servlet.annotation.WebListener;
    import javax.servlet.http.HttpSession;
    import javax.servlet.http.HttpSessionEvent;
    import javax.servlet.http.HttpSessionListener;
    import java.util.Map;
    
    /** * @program: ServletDom * @description: 登录的session的监听器 * @author: 高天乐 * @create: 2020-07-23 00:33 **/
    @WebListener
    public class LoginListener implements HttpSessionListener { 
        @Override
        public void sessionCreated(HttpSessionEvent httpSessionEvent) { 
    
        }
    
        @Override
        public void sessionDestroyed(HttpSessionEvent httpSessionEvent) { 
            System.out.println("销毁session");
            //创建上下文对象
            ServletContext sc = httpSessionEvent.getSession().getServletContext();
            //创建session对象
            HttpSession session = httpSessionEvent.getSession();
            //获取map
            Map<String,String> map = (Map<String, String>) sc.getAttribute("loginMap");
            //获取去用户账号
            String username = (String) session.getAttribute("username");
            //去掉当前用户
            map.remove(username);
            //重新绑定map
            sc.setAttribute("loginMap",map);
        }
    }