Java查询SQL to JSON仅返回一行

import java.sql.*;
import org.json.JSONObject;

public class SQLToJsonExample {
    public static void main(String[] args) {
        // JDBC连接信息
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String username = "root";
        String password = "password";

        try {
            // 连接数据库
            Connection connection = DriverManager.getConnection(url, username, password);

            // 执行SQL查询
            String sql = "SELECT * FROM mytable";
            Statement statement = connection.createStatement();
            ResultSet resultSet = statement.executeQuery(sql);

            // 转换为JSON格式
            if (resultSet.next()) {
                JSONObject json = new JSONObject();
                ResultSetMetaData metaData = resultSet.getMetaData();
                int columnCount = metaData.getColumnCount();
                for (int i = 1; i <= columnCount; i++) {
                    String columnName = metaData.getColumnName(i);
                    Object value = resultSet.getObject(i);
                    json.put(columnName, value);
                }

                // 输出JSON数据
                System.out.println(json.toString());
            }

            // 关闭连接
            resultSet.close();
            statement.close();
            connection.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}