I try this :

Criteria criteria = session.createCriteria(AbstractClass.class);
criteria.setResultTransformer(CriteriaSpecification.ROOT_ENTITY);

return criteria.uniqueResult();

where

@Inheritance(strategy = InheritanceType.JOINED)
abstract class AbstractClass ...

@Entity
class ConcretA extends AbstractClass { ... }

@Entity
class ConcretB extends AbstractClass { ... }

but the criteria query return a proxy of AbstractClass, not a ConcretA or ConcretB instance.

Why ?