Re: [eclipselink-users] JPA, OSGI, Eclipselink, class loaders

[Tom Ware <tom.ware@xxxxxxxxxx>]

Hi Teemu,

  Have you had a look at the Eclipse Gemini project?  It will be the Reference 
Implementation for the OSGi Java EE specifications.

http://www.eclipse.org/gemini/

  There is a sub-project for JPA support.  The documentation is sparse at the 
moment, but the mailing lists and newsgroups have pretty good response are are 
likely the best way to get advice about how to get started.

  Since this project is based on the actual specification, I suspect that JPA 
providers that want to provide OSGi services will migrate to work based on Gemini.

-Tom

teemu kanstren wrote:
> Dear all,
>
>  I have been trying to get my OSGI stuff to work with using JPA. As I am 
> sure many here know, I need to create the EntityManagerFactory 
> with  Persistence.createEntityManagerFactory("my-factory"). Now, behind 
> the scenes (am I supposed to read the sourcecode of the libraries as 
> well? :)) this loads the persistence.xml from the META-INF directory on 
> the classpath. With OSGI this always gives me the error 
> "javax.persistence.PersistenceException: No Persistence provider for 
> EntityManager named my-factory". After plenty of googling I came up with 
> the reason that the persistence.xml is loaded using ThreadContext 
> classloader, which in OSGI naturally fails. Reading up on it I also 
> found only suggestions to use EclipseLink since it is "the only one 
> build for OSGI and the JPA RI". Yet I get the same errors with it as well.
>
>  The only solution (after looong debugging sessions) I found that would 
> work is the one given 
> here:http://lsd.luminis.nl/jpa-persistence-in-osgi-with-openjpa/. That 
> is, to set the threadcontext classloader before call to 
> createEntityManagerFactory and reset it after. I use Apache Felix as the 
> OSGI container and I tried with both Hibernate JPA and EclipseLink JPA. 
> Same problem every time, yet outside OSGI it all works perfectly 
> (running the same code with JUnit). So, given that EclipseLink is the 
> JPA RI and targets an OSGI environment, maybe someone can give me some 
> answers here. My questions
>
> - Why is there no option in Persistence.createEntityManagerFactory() to 
> provide your own classloader to be used in loading of resources?
>
> - Why is the only error message you can get for this 
> the "javax.persistence.PersistenceException: No Persistence provider for 
> EntityManager named my-factory"? No mention of "unable to find 
> persistence.xml in classpath which is..." or "using classloaders..." or 
> whatever. Just "unable to find" is a pretty bad message since it should 
> know quite a bit more about why it is not able to find it (like missing 
> persistence.xml for some reason).
>
> Using the trick in the link above it all works fine. The only difference 
> with "for OSGI" in EclipseLink vs Hibernate I see is that I need to 
> import/export some stuff myself. Not much of an achievement considering 
> how cryptic it is to get it working at all. Am I missing something?
>
> Maybe there is some magic trick I miss since on the EclipseLink 
> documentation such 
> as http://wiki.eclipse.org/EclipseLink/Examples/OSGi/Developing_with_EclipseLink_OSGi_in_PDE it 
> all seems to be oh so easy. Or maybe Eclipse does some tricks behind the 
> scenes? Anyway, I was left thinking you can only run it inside Eclipse 
> as this is what is always used in the docs.
>
> To end more positively, thanks for all the efforts on JPA. Once I learn 
> it, and when it works, it is nice enough :)
>
> Teemu
>
>
>
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