检查db预准备语句中是否已存在用户名

import java.sql.*;

public class CheckUsername {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "dbuser";
        String password = "dbpass";
        String usernameToCheck = "exampleUser";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            String sql = "SELECT COUNT(*) FROM users WHERE username = ?";
            try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
                pstmt.setString(1, usernameToCheck);
                try (ResultSet rs = pstmt.executeQuery()) {
                    if (rs.next()) {
                        int count = rs.getInt(1);
                        if (count > 0) {
                            System.out.println("用户名已存在。");
                        } else {
                            System.out.println("用户名不存在。");
                        }
                    }
                }
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}