private Persistencia() {
        base = BaseDatos.getInstancia();
        base.conectar("jdbc:mysql://localhost/dda", "root", "1234");
    }


 public void conectar(String url,String u,String p){
        try {
            conexion = DriverManager.getConnection(url, u, p);
            stmt = conexion.createStatement();
        } catch (SQLException ex) {
            System.out.println("Error al conectar:" + ex.getMessage());
        }
    }

public Connection conexion() {
    if (conexion == null) {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conexion= DriverManager.getConnection("jdbc:mysql://"+host+"/"+bd, usuario, contrasena);
            System.out.println("exito");
        } catch (ClassNotFoundException | SQLException ex) {
            Logger.getLogger(conexionBD.class.getName()).log(Level.SEVERE, null, ex);
            System.out.println("error");
        }

    }
    return conexion;
}