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I had a similar but more general question about ORM and optimization, maybe you will find some clues and interesting remarks...

I would say only one EntityManager and persistance unit. Less cumbersome and no doubt about transaction configuration and integrity....

No, it will return the same reference again and again.

Dunno... JTA define the interface to any transaction mechanism implementation. It is not absolutly needed but maven dependencies require it.

My projects use Maven, and I need the following jar to be able to use transaction management in the simplest case (transaction on one local database):


jta
spring-tx
spring-aop
...

On my projects, I only inject EntityManager with @PersistenceContext annotation like this:



@PersistenceContext
private EntityManager entityManager;


EntityManagerFactory is...

It's dependent of the deployment tool, please see the documentation (manager of apache tomcat, or maven, or IDE).

Try:



<mvc:view-controller path="/" view-name="redirect:/main"/>


Where main is the url to redirect.

Using Spring 3.0, you can use:



<mvc:view-controller path="/" view-name="redirect:/entry"/>

without stacktrace, difficult to help you....

Question 1: for composite key, you need to designate at least one of the following:


multiple @Id and an @IdClass (for a composite primary key)
one @EmbeddedId


Please see this page for...

(sorry if the following question is in the wrong forum: it seems web oriented but I think the problem is specific to the conversion mechanisms)

I have the following form:



<form:form...