Java, 온라인 시험 시스템용 사용자 등록 및 로그인 모듈 개발

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

public class UserRegistration {
  
  private static final String DB_URL = "jdbc:mysql://localhost:3306/examsystem";
  private static final String DB_USER = "root";
  private static final String DB_PASSWORD = "password";

  private static final String SQL_INSERT = "INSERT INTO users (username, password, email) VALUES (?, ?, ?)";

  public static void registerUser(String username, String password, String email) {
    try (Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
        PreparedStatement stmt = conn.prepareStatement(SQL_INSERT)) {
      stmt.setString(1, username);
      stmt.setString(2, password);
      stmt.setString(3, email);
      stmt.executeUpdate();
      System.out.println("User registered successfully!");
    } catch (SQLException e) {
      e.printStackTrace();
    }
  }

  public static void main(String[] args) {
    String username = "testuser";
    String password = "testpassword";
    String email = "testuser@example.com";
    registerUser(username, password, email);
  }
}

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

public class UserLogin {
  
  private static final String DB_URL = "jdbc:mysql://localhost:3306/examsystem";
  private static final String DB_USER = "root";
  private static final String DB_PASSWORD = "password";

  private static final String SQL_SELECT = "SELECT * FROM users WHERE username = ? AND password = ?";

  public static boolean loginUser(String username, String password) {
    try (Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
        PreparedStatement stmt = conn.prepareStatement(SQL_SELECT)) {
      stmt.setString(1, username);
      stmt.setString(2, password);
      ResultSet rs = stmt.executeQuery();
      return rs.next();
    } catch (SQLException e) {
      e.printStackTrace();
    }
    return false;
  }

  public static void main(String[] args) {
    String username = "testuser";
    String password = "testpassword";
    boolean loggedIn = loginUser(username, password);
    if (loggedIn) {
      System.out.println("User logged in successfully!");
    } else {
      System.out.println("Invalid username or password!");
    }
  }
}