I finally managed to look at this case, I guess I was scared a bit with
all the generics involved and such, :-)
On 16/02/12 02:37, Jeff Wang wrote:
Scenario:
User "owns" contacts via an unidirectional @ManyToOne JPA mapping on
Contact. Contact subclasses from a @MappedSuperclass called
UserResource.
What I would like to do:
an Interface called ISubResourceService<T extends UserResource> that
has a CXF annotation of:
public interface ISubResourceService<T extends UserResource> {
@GET
@Produces("application/json")
List<T> getAll(@PathParam("userId") Long userId)
throws DataNotFoundException;
}
After doing replacing List<T> with List<? extends UserResource> I got
the JSON provider picking the response object...So try that please next
and an Interface called IContactService extends
ISubResourceService<Contact> with contact specific annotations (such
as a class level @Path("/contact")) but no other (relevant to this
discussion) annotations or mappings.
finally, in the ideal world, the implementation:
public abstract class AbstractSubResourceService<T extends
UserResource> implements
ISubResourceService<T> {
@Override
public List<T> getAll(Long userId) throws DataNotFoundException {
<code deleted for brevity>
}
}
and of course: (ideally, no code other than the @Service for Spring to
pick it up need to go here)
@Service
public class ContactServiceImpl extends AbstractSubResourceService<Contact>
implements IContactService {
}
The problem with the above implementation is that I get the "No
message body writer has been found for response class ArrayList"
error, which essentially is the problem when returning generic
collections, probably because of type erasure.
The following also return message body writer issues:
2) have AbstractSubResourceService return a Response, using entity(new
GenericEntity(List<T>){}), (we'll call this implementation 2, the base
is implementation 1)
3) have ContactService implement a getAll with the return signature
List<Contact> whose only code is "return super.getAll(userId);"
(implementation 3)
4) have IContactService do an @Override getAll with a return value of
List<Contact> (interface 2, same results vs all 3 implementations)
5) have IContactService copy getAll's declaration (with all CXF
annotations) with a return value of List<Contact> (interface 3, same
results vs all 3 implementations)
6) interface 3, remove the declaration of getAll in
ISubResourceService (call this interface 4), implementation (1 or 2)
AND 3 (see below for 2 without 3)
The following generates a no matching method WebApplicationException:
7) interface 4, implementation 1 or 2 (without 3)
The following works:
8) interface 4, implementation 3.
Based upon the above results:
1) GenericEntity is pointless if you are returning a generic
collection. (implementation 2 never worked, in any form)
2) having a sub interface "override" a super interface does not work
on an annotation basis (interface 2 and 3 does not work) possibly due
to retention when compiling?
3) I'm not quite sure why #7 returned no matching method. Is there an
annotation retention issue that causes CXF not to "see" that the
getAll in AbstractSubResourceService has applicable annotations in
IContactService? (never mind that it's truly horrendous coding style.)
So anyways, I've got code that works, but isn't particularly ideal.
If anyone can shed light on how they've done similar work, or
suggestions, I'd be happy to try them out. Sergey, could you shed some
light on results 2 and 3?
Please try as suggested above and see what happens to points 1-8 - it's
difficult for me to go through this list without seeing the concrete
code samples. There could be some issues there still when dealing will
complex hierarchies involving generics - so if you can help me to narrow
then down by posting a hierarchy example per every issue found then it
would be super
Thanks Sergey
thanks
Jeff
--
Sergey Beryozkin
Talend Community Coders
http://coders.talend.com/
Blog: http://sberyozkin.blogspot.com
