easy-crypto | WIP module aimed at providing a safer , easier to use | Cryptography library

Per spec, your manager EJB finds all entities and loads then into the returned List, but JPA defaults lists - such as classifications in your entity - as lazy loaded fields.

When your findAll method returns, there is no more transaction and the entities inside the lists became detached from the EntityManager. As such, the entity manager can't to load the contents of each classifications field to allow serialization.

You may change the behavior of your entity manager using some internal properties or even define your classifications field as eager fetched, but this may induce performance problems when you use the TrainingCenterEntity without accessing the classifications field (the classifications will be retrieved from database every time you get a center).

Your best approach is changing your named query to use JOIN FETCH: