JPA and Entity manager.

Question

Hi all,
I have a "simple" question:
Should I create a class to manage entity manager and entity manager factory on JPA2?
Why do I ask that? Because I read on J2EE tutorial:
With a container-managed entity manager, an EntityManager instance’s persistence context is automatically propagated by the container to all application components that use the EntityManager instance within a single Java Transaction Architecture (JTA) transaction.
To obtain an EntityManager instance, inject the entity manager into the application component:
@PersistenceContext
EntityManager em;
I'm using JSF2, JPA2, JTA and Glassfish3.1 on the NetBeans 7.0.1.
The wizard that creates the JSF's pages from entity class does a good work but I have some problem in the other classes.
When I call EntityManager it returns null!
The strange thing is that it works properly the first time, when I recall the EntityManager from another xhtml page and from another class the entity manager returns NULL!
So I would understand if the creation of a class for manage the EntityManagerFactory and EntityManager could help me.
Thank you for your future help!

Answer 1

Filippo Tenaglia wrote:
Hi all,
I have a "simple" question:
Should I create a class to manage entity manager and entity manager factory on JPA2?That question is far from complete, as the answer to this one is "depends on what you want to do!"
Why do I ask that? Because I read on J2EE tutorial:
With a container-managed entity manager, an EntityManager instance’s persistence context is automatically propagated by the container to all application components that use the EntityManager instance within a single Java Transaction Architecture (JTA) transaction.
To obtain an EntityManager instance, inject the entity manager into the application component:
@PersistenceContext
EntityManager em;
Given this information...
I'm using JSF2, JPA2, JTA and Glassfish3.1 on the NetBeans 7.0.1.That answer to your question is "NO", because you have a container available to you that can do the work (Glassfish). It makes no sense using Glassfish and then purposely ignoring the features it has to offer.
Lets get back to basics: you are doing something wrong here. You have to figure out what, you can only do that if you keep studying and getting a more complete understanding. If you are having trouble realizing that, perhaps you should start over without the help of any wizard at all; wizards are only useful when you are already experienced, right now the fact that code is generated is hindering you a lot because you will have a strong impulse to believe there can be no mistake; unfortunately there is no such safety net. The fact that you used the word "weird" is enough proof of this by the way. There is nothing weird here, just a mistake being made that has to be corrected.
And for the future: what IDE (Netbeans in your case) you use to develop really makes absolutely no difference at all. What is more interesting is which version of Java your are using, which can likely be Java 6 or Java 7 nowadays.