jpa异常No entity found for query问题解决

@SuppressWarnings({ "unchecked", "RedundantCast" })
	public X getSingleResult() {
		try {
			final Listresult = query.list();

			if ( result.size() == 0 ) {
				NoResultException nre = new NoResultException( "No entity found for query" );
				getEntityManager().handlePersistenceException( nre );
				throw nre;
			}
			else if ( result.size() > 1 ) {
				final SetuniqueResult = new HashSet(result);
				if ( uniqueResult.size() > 1 ) {
					NonUniqueResultException nure = new NonUniqueResultException( "result returns more than one elements" );
					getEntityManager().handlePersistenceException( nure );
					throw nure;
				}
				else {
					return uniqueResult.iterator().next();
				}
			}
			else {
				return result.get( 0 );
			}
		}
		catch (QueryExecutionRequestException he) {
			throw new IllegalStateException(he);
		}
		catch( TypeMismatchException e ) {
			throw new IllegalArgumentException(e);
		}
		catch (HibernateException he) {
			throw getEntityManager().convert( he );
		}
	}

Listlist=entityManager().createQuery("SELECT o FROM User o where o.userId=?1", User.class)
        		.setParameter(1, userId)
        		.getResultList();
        if(list!=null && list.size()!=0){
        	return list.get(0);
        }
        return null ;