Using the JPA2 CriteriaQuery API I'd like to just build the CriteriaQuery objects once for my DAO in an initialization method and then call EntityManager.createQuery(CriteriaQuery) each time I need to actually execute the query. From my testing this appears to work just fine but the docs and spec say nothing about CriteriaQuery's re-usability or thread safety. Any thoughts here?

Also is there any appreciable different in the amount of runtime HQL/SQL generation work that Hibernate has to do when using CriteriaQuery versus @NamedQuery? It seems like it is a reasonable thought to want to avoid re-parsing the query structure every time the DAO method is called.

This is really an interesting question, I would not expect any of the criteria classes to be thread-safe since there is nothing mentioned in the specification about this. At least you create the CriteriaBuilder using the persistence context which is definitely not thread-safe!
Hibernate has it's own DetachedCriteria for this area and I think this is simply not covered in the current JPA spec (yet).

regards,

Robin.

Well you can also create them from a CriteriaBuilder on the EntityManagerFactory which is thread-safe. Looking at the code (and doing some basic testing) indicates that this approach does work. There doesn't appear to be any state stored in the CriteriaQuery other than a reference to the EntityManagerFactory which makes me think this is ok.

It would be even better if JPA allowed for pre-compilatioon of the queries as well. One of the nice things about he @NamedQuery annotations is Hibernate does all the JPQL/HQL parsing and SQL generation during initialization so there is never a run-time cost.

The CDI 1.1 specification shows an example which does re-use a CriteriaQuery (section 1.3.1, JSF example) but the Spring Data guys had to synchronize access to a shared CriteriaQuery, see https://jira.spring.io/browse/DATAJPA-396.
So it seems that it's currently not safe to re-use a CriteriaQuery without proper synchronization. It's a pity that the JPA spec isn't clearer in this case.