java - 我的程序无法正常工作，为什么它不能正确读取用户名和密码？

Question

我正在为我的程序制作一个登录系统。我将帐户信息存储在 MySQL 数据库中。该数据库设置有一个名为“帐户”的表，其中包含两列:用户名和密码。我将 test 作为用户名，password 作为密码。输入正确的用户名和密码后，实际的程序应该打开。

这是我的问题。当我输入用户名和密码的任何信息时，程序将打开。不管它是否有效。发生的另一件事是，当我没有设置任何信息时，程序表示无法连接到数据库。这是连接数据库的问题吗？

package xyz.mrshawn.ezsniper;

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextArea;
import javax.swing.SwingConstants;

public class LoginMenu {

private JFrame frmEzsniperLogin;
String username;
String password;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                LoginMenu window = new LoginMenu();
                window.frmEzsniperLogin.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public LoginMenu() {
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frmEzsniperLogin = new JFrame();
    frmEzsniperLogin.setTitle("EzSniper : Login");
    frmEzsniperLogin.setBounds(100, 100, 353, 300);
    frmEzsniperLogin.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frmEzsniperLogin.getContentPane().setLayout(null);

    JLabel lblWelcomeToEzsniper = new JLabel("Welcome to EzSniper! Please login!");
    lblWelcomeToEzsniper.setForeground(Color.RED);
    lblWelcomeToEzsniper.setFont(new Font("Sylfaen", Font.PLAIN, 20));
    lblWelcomeToEzsniper.setHorizontalAlignment(SwingConstants.CENTER);
    lblWelcomeToEzsniper.setBounds(10, 11, 317, 33);
    frmEzsniperLogin.getContentPane().add(lblWelcomeToEzsniper);

    JLabel usernameLabel = new JLabel("Username:");
    usernameLabel.setFont(new Font("Trebuchet MS", Font.PLAIN, 15));
    usernameLabel.setBounds(10, 68, 82, 26);
    frmEzsniperLogin.getContentPane().add(usernameLabel);

    JLabel passwordLabel = new JLabel("Password:");
    passwordLabel.setFont(new Font("Trebuchet MS", Font.PLAIN, 15));
    passwordLabel.setBounds(10, 105, 82, 26);
    frmEzsniperLogin.getContentPane().add(passwordLabel);

    JTextArea usernameArea = new JTextArea();
    usernameArea.setFont(new Font("Monospaced", Font.PLAIN, 13));
    usernameArea.setBounds(102, 71, 115, 22);
    frmEzsniperLogin.getContentPane().add(usernameArea);

    JTextArea passwordArea = new JTextArea();
    passwordArea.setBounds(102, 108, 115, 22);
    frmEzsniperLogin.getContentPane().add(passwordArea);

    JButton loginButton = new JButton("LOGIN");
    loginButton.setFont(new Font("Sitka Heading", Font.PLAIN, 40));
    loginButton.setBounds(88, 176, 161, 46);
    loginButton.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            try {
                username = usernameArea.getText();
                password = passwordArea.getText();
            } catch (NullPointerException ex) {
                System.err.println("Please enter your username and password!");
                return;
            }

            Connection con;
            PreparedStatement ps;
            try {

                con = DriverManager.getConnection("jdbc:mysql://sql9.freemysqlhosting.net:3306/sql9268088", "censored", "censored");
                ps = con.prepareStatement("SELECT `username`, `password` FROM `accounts` WHERE `username` = ? AND `password` = ?");
                ps.setString(1, username);
                ps.setString(2, password);

                ResultSet result = ps.executeQuery();
                if (result.next()) {
                    JOptionPane.showMessageDialog(null, "Invalid username or password!", "ERROR", JOptionPane.WARNING_MESSAGE);
                } else {
                    CreateGUI.main(null);
                    System.out.println(username);
                }

            } catch (Exception ex) {
                JOptionPane.showMessageDialog(null, "Unable to connect to account database!", "ERROR", JOptionPane.WARNING_MESSAGE);
            }

        }
    });
    frmEzsniperLogin.getContentPane().add(loginButton);
}
}

Answer 1

你的逻辑已经倒退了...

if (result.next()) {
    JOptionPane.showMessageDialog(null, "Invalid username or password!", "ERROR", JOptionPane.WARNING_MESSAGE);
} else {
    CreateGUI.main(null);
    System.out.println(username);
}

它显示，“如果有结果，则显示错误消息，否则打开程序”

将 if (result.next()) { 更改为 if (!result.next()) { 或切换每个分支的内容

if (result.next()) {
    CreateGUI.main(null);
    System.out.println(username);
} else {
    JOptionPane.showMessageDialog(null, "Invalid username or password!", "ERROR", JOptionPane.WARNING_MESSAGE);
}