Hi Dan
I've started doing some work in this area and at the moment some manual
top-level element start/end serialization is being done.
I'd like to experiment a bit with using a generated Collection wrapper, for the
deserailzation to work too, but I'm kind of stuck a
bit as JAXB complains, while serializing this generated Collection instance
that no context is available for say Foo.class, for ex :
List<Object> foos = new ArrayList<Object>();
foos.add(new Foo());
Collection c = new Collection();
c.getAny().addAll(foos);
// marshal this collection instance
perhaps the solution is to create a shared JAXBContext for both Foo & Collection, but is it the right approach ? My concern is that
given that in JAX-RS we don't know in advance all the types we may have to deal with due to the dynamic subresource resolution, we
may end up with contexts for Foo & Collection, Bar & Collection, etc - though may be it's unlikely to happen in practice...
Dan K, Benson - is there any trick I may need to be aware to make it work in
the most efficient way ?
thanks, Sergey
Hi,
I'm writing a JAX-RS app and using CXF as the implementation. I was having
trouble wiring up some of my methods -- specifically, one that was to return
a list of people:
@GET
@Path("/list")
List<Person> getPersons();
Trying to run that, I got NPEs, as List can't be written out as a root
element by default.
A lot of the advice that I saw involved adding extra collections, and
changing the method signature to return the JAXBtized collection wrapper.
Since this isn't strictly a REST call, this either means that everybody
using the service call will have to unwrap the collection, or that I will
have to code two methods every time I want to return a collection.
Instead, I'd like to actually fix this in the providers at the core of CXF.
I created a collection object of my own:
<complexType name="Collection">
<sequence>
<any minOccurs="0" maxOccurs="unbounded"></any>
</sequence>
</complexType>
... And then overrode the JAXBElementProvider.writeTo method:
package us.XXXXXXXXX.iotool.jaxrs;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import org.apache.cxf.jaxrs.provider.JAXBElementProvider;
import us.XXXXXXXXX.iotool.model.Collection;
public class CollectionJAXBElementProvider extends JAXBElementProvider {
@Override
public void writeTo(Object obj, Class<?> cls, Type genericType,
Annotation[] anns, MediaType m,
MultivaluedMap<String, Object> headers, OutputStream os)
throws IOException {
try {
Object actualObject = checkAdapter(obj, anns, true);
// if it's a java.util.Collection, wrap it in our collection object
if (actualObject instanceof java.util.Collection) {
us.XXXXXXXXX.iotool.model.Collection collection = new Collection();
java.util.List list =
new java.util.ArrayList<Object>((java.util.Collection)actualObject);
collection.setAnies(list);
actualObject = collection;
}
// now pass to the superclass
super.writeTo(actualObject, cls, genericType, anns, m, headers, os);
} catch (WebApplicationException e) {
throw e;
} catch (Exception e) {
throw new WebApplicationException(e);
}
}
}
This works fine -- any java.util.Collection will get wrapped in a
<Collection> tag.
There are a couple of downsides here:
(1) Doing it in this provider means that it doesn't apply to my JSON
provider.
(2) I don't think that I have a great way to consume this on the client side
as anything other than a wrapped collection (if that even works).
Two sets of questions:
(1) Can I get to my desired end -- transparently handling
java.util.Collection objects -- without all this mucking about? Can I do
this with a XmlJavaTypeAdapter?
(2) Is there a different spot in the chain where I can put this that would
change the objects prior to their being consumed by any providers? The
documentation on the JAX-RS filters wasn't totally clear to me on this
point.
Thanks in advance,
Dan
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