用java编写，运用数据访问层、业务逻辑层、UI层三层架构设计完成用户登录业务设计。给出代码

好的，以下是一个基于三层架构的用户登录业务的 Java 代码示例：

UserDao.java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class UserDao {
    private static final String URL = "jdbc:mysql://localhost:3306/mydb";
    private static final String USER = "root";
    private static final String PASSWORD = "password";

    public User login(String username, String password) {
        User user = null;
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            conn = DriverManager.getConnection(URL, USER, PASSWORD);
            String sql = "SELECT * FROM user WHERE username = ? AND password = ?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                user = new User();
                user.setId(rs.getInt("id"));
                user.setUsername(rs.getString("username"));
                user.setPassword(rs.getString("password"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (rs != null) {
                    rs.close();
                }
                if (pstmt != null) {
                    pstmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return user;
    }
}

UserService.java

public class UserService {
    private UserDao userDao = new UserDao();

    public User login(String username, String password) {
        User user = userDao.login(username, password);
        if (user == null) {
            System.out.println("Invalid username or password.");
        }
        return user;
    }
}

LoginFrame.java

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class LoginFrame extends JFrame {

    private JPanel contentPane;
    private JTextField textFieldUsername;
    private JTextField textFieldPassword;
    private UserService userService = new UserService();

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    LoginFrame frame = new LoginFrame();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public LoginFrame() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        JLabel lblUsername = new JLabel("Username");
        lblUsername.setBounds(63, 76, 86, 14);
        contentPane.add(lblUsername);

        JLabel lblPassword = new JLabel("Password");
        lblPassword.setBounds(63, 119, 86, 14);
        contentPane.add(lblPassword);

        textFieldUsername = new JTextField();
        textFieldUsername.setBounds(159, 73, 180, 20);
        contentPane.add(textFieldUsername);
        textFieldUsername.setColumns(10);

        textFieldPassword = new JTextField();
        textFieldPassword.setBounds(159, 116, 180, 20);
        contentPane.add(textFieldPassword);
        textFieldPassword.setColumns(10);

        JButton btnLogin = new JButton("Login");
        btnLogin.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                String username = textFieldUsername.getText();
                String password = textFieldPassword.getText();
                User user = userService.login(username, password);
                if (user != null) {
                    JOptionPane.showMessageDialog(LoginFrame.this, "Login success.");
                }
            }
        });
        btnLogin.setBounds(159, 167, 89, 23);
        contentPane.add(btnLogin);
    }

}

上面的代码示例中，User 表示用户实体类，包含 id、username 和 password 三个属性。UserDao 类实现了与用户相关的数据库操作，例如 login 方法用于验证用户登录信息。UserService 类实现了用户登录的业务逻辑，例如 login 方法用于处理用户登录逻辑。LoginFrame 类实现了用户登录界面，包含用户名和密码输入框、登录按钮等组件。当用户点击登录按钮时，会调用 UserService 类中的 login 方法来处理用户登录逻辑，并根据返回结果显示相应的信息。

注意，在实际开发中，我们还需要考虑异常处理、安全性、性能等方面的问题。上面的代码示例仅供参考。