The QueryDSL library offers a fluent interface for building type safe (JPA) queries. The API looks a lot smoother than the JPA Criteria API so that an integration would be quite a cool thing. I can imagine collaboration in the following areas:
We could offer an alternative to the standard JPA Criteria API based Specifications as the implementations should become much nicer with Querydsl. So we could have something like this:
We could create a QueryDsl specific subclass of SimpleJpaRepository and use this subclass in case the entity specific repository interface implements this 'mixin' so to speak.
To ease building queries with QueryDsl we could provide a base class that gets an EntityManager injected and allows to create queries via a helper method. This class could be used for custom repository implementations then.