public class Conexion {

 private Connection con;
 private final String driver = "com.mysql.cj.jdbc.Driver";
 private final String usuario = "TestBD";
 private final String contrasena = "pass";
 private final String urlBaseDatos = "jdbc:mysql://localhost:3306/TestBD?serverTimezone=UTC";

 private static Conexion conexion;

 private Conexion(){}

 public static Conexion getInstance() throws SQLException{
    if(conexion == null){
        conexion = new Conexion();
    }
    conexion.conectar();
    return conexion;
 }

 private void conectar() throws SQLException{
     if (con == null || con.isClosed()) {
         try {
         Class.forName(driver);
         } catch (ClassNotFoundException ex) {
         Logger.getLogger(Conexion.class.getName()).log(Level.SEVERE, null, ex);
         }
         con = DriverManager.getConnection(urlBaseDatos, usuario, contrasena);
     }
 }

 public boolean existeConexion() throws SQLException{
     return con != null && !con.isClosed();
 }

 public Connection getCon() {
     return con;
 }
}

public class TestConexion {
 public static void main(String[] args){
     try {
         if(Conexion.getInstance().existeConexion()){
             System.out.println("Conexión Establecida");
         }
     } catch (SQLException ex) {
         Logger.getLogger(TestConexion.class.getName()).log(Level.SEVERE, null, ex);
         System.out.println("Error al Establecer la Conexión");
     }
 }
}