public static void removeAllInstances(final Class<?> clazz) {
	    
		SessionFactory sessionFactory =new Configuration().configure().buildSessionFactory();
	    
		Session session = sessionFactory.getCurrentSession();       
	    session.beginTransaction();
	    final List<?> instances = session.createCriteria(clazz).list();
	    for (Object obj : instances) {
	        session.delete(obj);
	    }
	    session.getTransaction().commit();
	}	

...

   	        EntityManagerFactory emf = Persistence.createEntityManagerFactory(".блабалбла");
		
		EntityManager em = emf.createEntityManager();
		
		EntityTransaction tx = em.getTransaction();
		
		tx.begin();
		
		removeAllInstances(балбла.class);