Injecting entity manager into managed bean

问题

It is possible to inject entity manager (or its factory) into jsf managed bean using @PersistenceContext (or @PersistenceUnit)?

I Tried it but nothing, I obtain a NullPointerException.

回答1:

Yes it is possible. This is the syntax.

@PersistenceContext
EntityManager em;

You need to have a persistence.xml in your project. Btw: I'm running Glassfish 3.

After this you can then use methods like em.createNamedQuery.

Also remember the injection takes place after the constructor so if your trying to do database functions in the constructor this will not work. You will have to add the @PostConstruct annotation to a method. This is probably the problem your having.

来源：https://stackoverflow.com/questions/4727920/injecting-entity-manager-into-managed-bean