有了 JPA，是否还需要使用 EJB session bean？

Question

What are some use cases for using session beans? I personally prefer to hold session status in web tire when the requests need to be 'sticky". Thanks.

Answer 1

Note that some JPA concepts are tied to other JavaEE concepts and in some cases EJB. Specifically, Container-Managed EntityManagers injected via @PersistenceContext

• @PersistenceContext(type = EXTENDED) EntityManager em;
  • EntityManager is linked to and only usable by a @Stateful session bean
• @PersistenceContext(type = TRANSACTION) EntityManager em;
  • EntityManager is linked to and only usable within the scope of the current running JTA transaction

In the first case an EJB is necessary. In the second case, an EJB is nice to take care of the transaction plumbing automatically.

Answer 2

All the services provided by a session bean (declarative transactions, declarative security, asynchronous methods, timers, etc.). If you don't need any of those services, then you don't need session beans.

Answer 3

The main use case is to avoid having to write the tedious and verbose transaction management code that required for JPA.

With EJB this becomes nearly always invisible and at most a single extra annotation.