ConexionSingleton.java

package org.example.util;

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

public class ConexionSingleton {
    private static String url = "jdbc:mysql://localhost:3306/java_curso";
    private static String username="root";
    private static String password="";
    private static Connection connection;

    public static Connection getInstance() throws SQLException {
            if(connection==null){
                connection = DriverManager.getConnection(url, username, password);
            }
            return connection;
    }
}

Example.java

package org.example;

import org.example.util.ConexionSingleton;
import java.sql.*;

public class EjemploJdbc {

    public static void main(String[] args) {


        try (Connection conn = ConexionSingleton.getInstance();
             Statement stmt = conn.createStatement();
             ResultSet resultado = stmt.executeQuery("SELECT * FROM productos")){

                while (resultado.next()){
                    System.out.println(resultado.getInt("id"));
                    System.out.println(resultado.getString("nombre"));
                    System.out.println(resultado.getInt("precio"));
                    System.out.println(resultado.getDate("fecha_registro"));
                }

        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
}