如何解决JPA-CriteriaAPI的Java警告和编译错误？

Question

If I declare like following it gives compilation error as follows :

Answer 1

ParameterExpression<List<?>> vp=cb.parameter(List.class);

如果不起作用，请保留原始类型并添加@SuppressWarning('rawtypes');

Answer 2

Please make sure that your question should have all the information which will convey your problem statment very clearly. What I can guess from above image is that your are facing problem while creating ParameterExpression. And for that you can take a look at following sample code.

private List<Customer> findCustomerWithParam(String name) {
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Customer> criteriaQuery = cb.createQuery(Customer.class);
Root<Customer> customer = criteriaQuery.from(Customer.class);
ParameterExpression<String> nameParameter = cb.parameter(String.class, "name");
criteriaQuery.select(customer).where(cb.equal(customer.get("name"), nameParameter));
return em.createQuery(criteriaQuery).setParameter("name", name).getResultList();

}

Hope this might help you.

Answer 3

The problem stems using the following pattern

public <T> T f(Class<T> type) {
    return type.newInstance();
}

This does not yet work satisfactory for container classes. An inefficient work-around would be to copy the list.

List<?> list0 = f(List.class);
List<String> list = list0.stream()
        .map(Objects::toString)
        //Or .map(s -> (String)s)
        .collect(Collectors.toList());

So it is an API restriction. I confess not being aware that the method parameter could deliver.