public class EntityManagerHelper {
	public static <ENTITY_TYPE> void persistInTransaction(EntityManager entityManager, ENTITY_TYPE entity) {
		executeInTransaction(entityManager, () -> entityManager.persist(entity));
	}

	public static <EC> void removeAll(EntityManager em, Class<EC> entityClass) {
		executeInTransaction(em, () -> {
			List<EC> all = findAll(em, entityClass);
			for (EC entity : all) {
				em.remove(entity);
			}
		});
	}

	public static <EC> List<EC> findAll(EntityManager em, Class<EC> entityClass) {
		CriteriaBuilder cb = em.getCriteriaBuilder();
		CriteriaQuery<EC> criteria = cb.createQuery(entityClass);
		criteria.from(entityClass);
		return em.createQuery(criteria).getResultList();
	}

	private static void executeInTransaction(EntityManager entityManager, TransactionExecutor transactionExecutor) {
		try {
			entityManager.getTransaction().begin();
			transactionExecutor.executeInTransaction();
			entityManager.getTransaction().commit();
		} catch (RuntimeException e) {
			if (entityManager.getTransaction().isActive()) {
				entityManager.getTransaction().rollback();
			}
			throw e;
		}
	}

	@FunctionalInterface
	public interface TransactionExecutor {
		void executeInTransaction();
	}
}