java基础之登录程序

注：此版本仅供学习使用！

Login.java

import java.awt.Font;
import java.awt.event.*;
import java.sql.*;

import javax.swing.*;
import javax.swing.border.EmptyBorder;

@SuppressWarnings("serial")
public class Login extends JFrame {
    JLabel jla_tips;
    JLabel jla_username;
    JTextField jtf_username;
    JLabel jla_password;
    JPasswordField jpf_password;
    JButton jbt_login;
    JButton jbt_cancel;
    int count=0;

    public Login() {
        ImageIcon icon = new ImageIcon("images/favicon.png");
        setIconImage(icon.getImage());

        JPanel contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        jla_tips = new JLabel();
        jla_tips.setBounds(155, 40, 200, 25);
        contentPane.add(jla_tips);

        jla_username = new JLabel("用户名:");
        jla_username.setBounds(80, 70, 60, 25);
        contentPane.add(jla_username);

        jtf_username = new JTextField();
        jtf_username.setHorizontalAlignment(JTextField.LEFT);
        jtf_username.setBounds(150, 70, 150, 25);
        contentPane.add(jtf_username);
        
        jla_password = new JLabel("密  码:");
        jla_password.setBounds(80, 120, 60, 25);
        contentPane.add(jla_password);
        
        jpf_password = new JPasswordField();
        jpf_password.setBounds(150, 120, 150, 25);
        contentPane.add(jpf_password);
        
        // 登录按钮
        jbt_login = new JButton("登录");
        jbt_login.setFocusPainted(false);
        jbt_login.setBounds(150, 170, 70, 30);
        contentPane.add(jbt_login);
        jbt_login.addActionListener(new loginListener());
        jpf_password.addActionListener(new loginListener());

        // 置空按钮
        jbt_cancel = new JButton("取消");
        jbt_cancel.setFocusPainted(false);
        jbt_cancel.setBounds(235, 170, 70, 30);
        contentPane.add(jbt_cancel);
        jbt_cancel.addActionListener(new cancelListener());
        
        // 背景图
        Icon login3 = new ImageIcon("images/login3.jpg");
        JLabel jla_login3 = new JLabel(login3);
        jla_login3.setBounds(0, 0, 450, 300);
        contentPane.add(jla_login3);
        
        // 字体设置
        Font fontstr = new Font("宋体", Font.PLAIN, 14);
        jla_username.setFont(fontstr);
        jla_password.setFont(fontstr);
        jla_tips.setFont(fontstr);
        jbt_login.setFont(fontstr);
        jbt_cancel.setFont(fontstr);

        setTitle("登录");
        setSize(450, 300);
        setLocationRelativeTo(null);
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public class cancelListener implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent arg0) {
            jtf_username.setText(null);
            jpf_password.setText(null);
        }
        
    }
    public class loginListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            String username = jtf_username.getText().trim();
            char[] values = jpf_password.getPassword();
            String password = new String(values);
            if (username != null && username.length() != 0 && password != null
                    && password.length() != 0) {
                try {
                    // 1.注册驱动
                    Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
                    // 2.建立连接
                    // 2.1连接串
                    String DBurl = "jdbc:sqlserver://localhost:1433;DatabaseName=JavaDB";
                    String DBname="sa";
                    String DBpwd="940523";
                    Connection con = DriverManager.getConnection(DBurl,DBname,DBpwd);
                    
                    // 创建会话
//                    Statement st = con.createStatement();
//                    String sql = "select count(*) as cnt from T_user where username='"
//                            + username + "' and password='" + password + "'";
//                    ResultSet rs = st.executeQuery(sql);
                    
                    /*
                     * 防止SQL注入
                     */
                    String sql = "select count(*) as cnt from T_user where username=? and password=?";
                    PreparedStatement st = con.prepareStatement(sql);
                    st.setString(1, username);
                    st.setString(2, password);
                    String sql2 = "select count(*) as cnt from T_user where username=?";
                    PreparedStatement st2 = con.prepareStatement(sql2);
                    st2.setString(1, username);
                    // 结果集
                    ResultSet rs = st.executeQuery();
                    ResultSet rs2 = st2.executeQuery();

                    rs.next();
                    rs2.next();
                    if (rs.getInt("cnt") > 0) {
                        setVisible(false);
                        new Hello();
                    } else if (rs2.getInt("cnt") == 0) {
                        JOptionPane.showMessageDialog(null, "无该用户!");
                    }else {
                        jla_tips.setText("密码错误!");
                        count++;
                        if(count==3){
                            JOptionPane.showMessageDialog(null, "登录失败超过三次!");
                            System.exit(0);
                        }
                    }
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            } else {
                if (username.length() == 0 && password.length() == 0)
                    jla_tips.setText("帐号与密码均不能为空!");
                else if (username.length() == 0)
                    jla_tips.setText("帐号不能为空!");
                else if (password.length() == 0)
                    jla_tips.setText("密码不能为空!");
            }
        }
    }

    public static void main(String[] args) {
        new Login();
    }
}

hello.java

import java.awt.Font;
import javax.swing.*;
import javax.swing.border.EmptyBorder;

@SuppressWarnings("serial")
public class Hello extends JFrame {
    JLabel jla_title;

    public Hello() {
        ImageIcon icon = new ImageIcon("images/favicon.png");
        setIconImage(icon.getImage());

        JPanel contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        jla_title = new JLabel();
        jla_title.setText("欢迎使用本软件!");
        jla_title.setBounds(120, 100, 200, 25);
        // 字体设置
        Font fontstr = new Font("宋体", Font.PLAIN, 26);
        jla_title.setFont(fontstr);
        contentPane.add(jla_title);

        setTitle("欢迎界面");
        setSize(450, 300);
        setLocationRelativeTo(null);
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    // public static void main(String[] args) {
    // new Hello();
    // }
}

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