If you are using the JPA’s standard specification implementation (Read : Introduction to JPA), then you would use EntityManagerFactory for opening the session. But, if you are using the hibernate implementation, you have hibernate specific SessionFactory for managing the sessions. Here there is lot of confusion between developers like which one is the best approach. Here, there is two opinions are popular:
- EntityManagerFactory is the standard implementation, it is the same across all the implementations. If we migrate our ORM for any other provider, there will not be any change in the approach for handling the transaction. In contrast, if you use hibernate’s session factory, it is tied to hibernate APIs and ca not migrate to new vendor easily.
- One dis-advantage of using the standard implementation is that, it is not providing the advanced features. There is not much control provided in the EntityManager APIs. Whereas, hibernate’s SessionFactory has lot of advanced features which can not done in JPA. One such thing is retrieving the ID generator without closing the transaction, batch insert, etc.
Looking into the above points, one has to decide which one is better. There is no hard rule, after all it depends on the developers requirement. Another suggestion is that, we can use entity manger and session factory together. In this approach, entity manage delegates session handling to the hibernate by invoking the unwrap method. Like this:
Session session = entityManager.unwrap(Session.class);
Using EntityManagerFactory approach allows us to use callback method annotations like @PrePersist, @PostPersist,@PreUpdate with no extra configuration. Using similar callbacks while using SessionFactory will require extra efforts.