Question

Our application consists of three parts:
1. A core module, which contains model and DAO classes and the spring configuration.
2. A web module, which uses the core package and is executed in a (portal) web environment.
3. A tasks module, which also uses the core package and is executed as a scheduled task (no web context)

We try to introduce the OpenEntityManagerInView pattern with the Spring Filter for the web module. As far as I understand it, the DAOs must not close the EntityManager because the filter does it. Furthermore, I would inject an EntityManager with @PersistenceContext instead of EntityManagerFactory with @PersistenceUnit (is that right?).

But how can I reuse the same core package with these modifications in the tasks module? There is no Filter which controles the lifecycle of the EntityManager.

Answer 1

OpenEntityManagerInViewFilter is usually used to complement Spring transaction management, as follows:

• You define transaction boundaries in your code. Inside a transaction you can use EntityManager injected with @PersistenceContext (or Hibernate session obtained from getCurrentSession()). Also transactions define JPA Units of Work, i.e. all changes to persistent object you made inside a transaction will be propageted to the database automatically.

• But sometimes you need to access the database outside of defined transaction (the most notable case is lazy loading when rendering a view). For this case you have OpenEntityManagerInViewFilter that allows you to access the database and use @PersistenceContext at any point during HTTP request processing.

As you can see, OpenEntityManagerInViewFilter acts as a substitute for absent transaction, therefore you can run the same code without OpenEntityManagerInViewFilter if you do it inside a scope of transaction. So, you need to define transactons appropriately to make sure that all persistence-related code in your tasks module runs inside a transaction.