public class HibernateUtil {

  private static SessionFactory sessionFactory;
  private static Session session;
	
  /**
   * Crea la factoria de sesiones
   */
  public static void buildSessionFactory() {

    Configuration configuration = new Configuration();
    configuration.configure();
    // Se registran las clases que hay que mapear con cada tabla de la base de datos
    configuration.addAnnotatedClass(Clase1.class);
    configuration.addAnnotatedClass(Clase2.class);
    configuration.addAnnotatedClass(Clase3.class);
    . . .
    
    ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder().applySettings(
      configuration.getProperties()).build();
    sessionFactory = configuration.buildSessionFactory(serviceRegistry);
  }
	
  /**
   * Abre una nueva sesión
   */
  public static void openSession() {
    session = sessionFactory.openSession();
  }
	
  /**
   * Devuelve la sesión actual
   * @return
   */
  public static Session getCurrentSession() {
	
    if ((session == null) || (!session.isOpen()))
      openSession();
			
    return session;
  }
	
  /**
   * Cierra Hibernate
   */
  public static void closeSessionFactory() {
	
    if (session != null)
      session.close();
		
    if (sessionFactory != null)
      sessionFactory.close();
  }
}