java判断登陆代码,java登录验证代码

java里面如何在用户登录管理页面时判断用户是否登录

给你详细讲一下。

比如系统有个登陆页面(login.jsp)：

name:_________

password:____________

(登陆按钮）

你按下登陆按钮，就根据name和password去数据库里面查，如果判断有此用户并且密码正确，就设置一个session的键对应的值，键名字自己取，统一即可，比如"userInfo"，代码就是servlet的doPost里面

HttpSession session = request.getSession();

Hashtable userInfo = new Hashtable();

userInfo.setAttribute("userName", request.getParameter("userName");

userInfo.setAttribute("passWords", Util.toSecret( request.getParameter("passWords)); //密码最好加密

session.setAttribute("userInfo", userInfo);

session是在一定时期（超时时间内）一直存在的，这段时间内你可以随时判断用户是否合法，否则就退回登陆页面。

在任何除了登陆页面以外的页面访问，只需判断有没有这个键值，没就到登陆页面，否则进正常页面。（最好写在servlet中，让servlet当页面控制器）代码如下：

if ( session.getAttribute("userInfo")==null ) {

response.sendRedirect(request.getServletContext.getPath() + "/login.jsp");

} else {

request.getRequestDispatcher("/正常页面.jsp").forward(request,response);

}

相关问答

Q1: java 如何做登录的判断？

public class LoginServlet extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet{//构造函数public LoginServlet(){super();}//服务器端的验证、提交处理 protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException{response.setContentType("text/html;charset=GB2312"); MD5_Encoding md5=new MD5_Encoding(); // 获取提交的用户名： String UserName = request.getParameter("logname"); // 获取提交的密码： String Password = request.getParameter("logpwd"); // 对密码进行MD5数据加密 String EnPwd =md5.getMD5ofStr(Password); String random = request.getParameter("random"); String random2 = request.getSession().getAttribute("random").toString(); if (!random.equals(random2)){request.setAttribute("error", "输入的验证码不正确！");try{request.getRequestDispatcher("Login.jsp").forward(request, response);}catch (Throwable t){getServletContext().log(t.getMessage());}}//核对用户名和密码，决定是否通过登陆验证 DB_User dbuser = new DB_User(); User user = dbuser.get(UserName, EnPwd); if (user != null){// 登录成功时,把strUserName设成session变量UserName request.getSession(true).setAttribute("username", UserName);try{request.getRequestDispatcher("Welcome1.jsp").forward(request,response);}catch (Throwable t){getServletContext().log(t.getMessage());}}else{// 否则为游客身份 request.getSession(true).setAttribute("username", UserName);try{request.getRequestDispatcher("Welcome1.jsp").forward(request, response);}catch (Throwable t){getServletContext().log(t.getMessage());}}}}一年前写的了 提交后,在JSP中再对username判断一下就OK了

Q2: 模拟一个简单的用户登陆程序，判断登录的用户名和密码是否正确，输出登录判断结果，用java怎么写？

package test;

import java.util.Scanner;

public class TestLogin {

private static final String USERNAME = "Tom";//此处定义用户名

private static final String PASSWORD = "123";//定义密码

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

System.out.print("请输入您的用户名:");

String username_in = sc.next();

System.out.print("请输入您的密码:");

String password_in = sc.next();

if(username_in.equals(USERNAME) password_in.equals(PASSWORD)){

System.out.println("登录成功");

}else{

System.out.println("用户名或密码错误");

}

}

}

这是从控制台输入的最简单的方法。

Q3: java登录验证源代码

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

public class Test_Login extends javax.swing.JFrame {

private JPanel jPanel1;

private JButton bntLogin;

private JButton bntCannel;

private JPasswordField pwd;

private JTextField username;

private JLabel jLabel2;

private JLabel jLabel1;

public static void main(String[] args) {

Test_Login inst = new Test_Login();

inst.setLocationRelativeTo(null);

inst.setVisible(true);

}

public Test_Login() {

super();

initGUI();

}

private void initGUI() {

try {

setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);

{

jPanel1 = new JPanel();

getContentPane().add(jPanel1, BorderLayout.CENTER);

jPanel1.setLayout(null);

{

jLabel1 = new JLabel();

jPanel1.add(jLabel1);

jLabel1.setText("用户名");

jLabel1.setBounds(45, 30, 75, 25);

}

{

jLabel2 = new JLabel();

jPanel1.add(jLabel2);

jLabel2.setText("密码");

jLabel2.setBounds(45, 75, 55, 15);

}

{

username = new JTextField();

jPanel1.add(username);

username.setBounds(100, 30, 140, 25);

}

{

pwd = new JPasswordField();

jPanel1.add(pwd);

pwd.setBounds(100, 70, 140, 25);

}

{

bntLogin = new JButton();

jPanel1.add(bntLogin);

bntLogin.setText("登陆");

bntLogin.setBounds(40, 120, 60, 30);

bntLogin.addMouseListener(new MouseAdapter() {

public void mouseClicked(MouseEvent e) {

if (username.getText().equals("lisong")

pwd.getText().equals("lisong")) {

JOptionPane.showMessageDialog(Test_Login.this,

"登录成功");

} else {

JOptionPane.showMessageDialog(Test_Login.this,

"登录失败");

}

}

});

bntCannel = new JButton();

jPanel1.add(bntCannel);

bntCannel.setText("取消");

bntCannel.setBounds(180, 120, 60, 30);

bntCannel.addMouseListener(new MouseAdapter() {

public void mouseClicked(MouseEvent e) {

System.exit(0);

}

});

}

}

pack();

setSize(300, 215);

} catch (Exception e) {

e.printStackTrace();

}

}

}