Hi Teemu,
On 03/02/2011 2:30 PM, teemu kanstren wrote:
Hello Shaun & Tom,
Thanks for your replies. I noted Gemini in my search but did
not pursue that further at that time. This is because JPA is
just one technology for me in building my software and I would
hope that it would not force me into a specific container
implementation. I think that's what a "standard" like JPA should
enable. However, I will try to keep an eye on this stuff since
it is interesting.
I am curious about the OSGI Java EE specifications you
mention. Can you point me to some links for further information
on what they are?
The document is the "OSGi Service Platform Release 4 Version 4.2
Enterprise Specification" which you can download from: http://www.osgi.org/Download/Release4V42
Is the JPA-PersistenceUnit header specific to EclipseLink?
Yes but in the spec the standard and portable header as supported by
Gemin JPA is "Meta-Persistence" (note you don't provide PU names but
rather persistence descriptor files--e.g. persistence.xml).
And is the classloader property also EclipseLink specific?
That is are they supported in general in OSGI containers/JPA
providers or just EclipseLink?
This is an EclipseLink feature but isn't always necessary.
I never noticed those before, thanks for clearing that up.
At least now I know how to make one JPA provider work in a more
"official way" if my current hack fails :) Maybe this stuff
could find a more explicit mention in the docs as well.
The OSGi spec as implemented by Gemini JPA is the "official way"
which is why Tom and I are gently pushing you in that direction. ;-)
Shaun
Teemu
2011/2/3 Shaun Smith <shaun.smith@xxxxxxxxxx>
Hi Teemu,
As Tom points out Gemini JPA will deliver OSGi compliant
JPA and that is where the future lies.
However the current EclipseLink support for JPA in OSGi is
not all that different from the OSGi spec and was
certainly drawn upon when the spec was being authored. As
you suggest, there are lots of "tricks behind the scenes"
to make JPA work in OSGi and EclipseLink is doing them.
:-) If you follow the instructions on the examples you'll
see what you have to do--which isn't all that much. The
key thing is declaring the JPA-PersistenceUnits header in
your bundle containing the persistence.xml. EclipseLink
locates persistence units (declared in persistence.xml) in
bundles using this header. In the OSGi spec this header
is "Meta-Persistence" and is used slightly differently but
the intent is the same.
Also, you can indeed pass a classloader to
EntityManagerFactory.createEntityManagerFactory and this
classloader will be used to resolve classes and metadata
but the persistence.xml *must* be declared using the
JPA-PersistenceUnit header. From http://wiki.eclipse.org/EclipseLink/Examples/OSGi/Equinox_Byte_Code_Weaving:
import org.eclipse.persistence.config.PersistenceUnitProperties;
...
Map<String,Object> properties = new HashMap<String, Object>();
properties.put(PersistenceUnitProperties.CLASSLOADER, this.getClass().getClassLoader());
emf = Persistence.createEntityManagerFactory("comics", properties);
This example also demonstrates how to run
outside Eclipse PDE.
Hope this helps,
Shaun
On 03/02/2011 9:10 AM, Tom Ware wrote:
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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Shaun Smith | Principal
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Phone: +1.905.502.3094 | Mobile: +1.416.558.6244
Oracle Fusion
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practices and products that help protect the
environment
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eclipselink-users mailing list
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_______________________________________________
eclipselink-users mailing list
eclipselink-users@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/eclipselink-users
--
Shaun Smith | Principal Product Manager
Phone: +1.905.502.3094 | Mobile: +1.416.558.6244
Oracle Fusion Middleware, TopLink
ORACLE Canada | 110 Matheson Boulevard West, Suite 100,
Mississauga, Ontario | L5R 3P4
Oracle is committed to developing practices and
products that help protect the environment
|
