Re: JSR311: Re: ContextResolver removal

From: Marc Hadley <Marc.Hadley_at_Sun.COM>
Date: Tue, 10 Jun 2008 10:53:13 -0400

Rather than updating the javadoc of a class that might get deleted,
here's an example from one of the Jersey samples:

public final class JAXBContextResolver implements
ContextResolver<JAXBContext> {

     private final JAXBContext context;

     private final Set<Class> types;

     private final Class[] cTypes = {Containers.class, Container.class,

     public JAXBContextResolver() throws Exception {
         this.types = new HashSet(Arrays.asList(cTypes));
         this.context = JAXBContext.newInstance(cTypes);

     public JAXBContext getContext(Class<?> objectType) {
         return (types.contains(objectType)) ? context : null;

The above application class supplies a JAXBContext for the three
classes Containers.class, Container.class and Item.class. This one
doesn't do much of interest but it could set a bunch of properties on
the JAXContext that affect the behavior of marshallers and
unmarshallers obtained from it.

The Jersey JAXB entity provider gets access to providers via an
injected instance:

     @Context private ContextResolver<JAXBContext> cr;

and uses this instance to look for an application supplied JAXBContext
for like this:

     protected final JAXBContext getJAXBContext(Class type) throws
JAXBException {
         if (cr != null) {
             JAXBContext c = cr.getContext(type);
             if (c != null) return c;

         // no application supplied context so create own

The injected ContextResolver is not actually an instance of the
application class JAXBContextResolver, rather it is an implementation-
supplied class that aggregates the set of Providers of a particular
kind (JAXContext in this example) and calls them one-by-one until one
of them returns a non-null context. If no application-supplied
provider return a non-null context then null is returned.


On Jun 10, 2008, at 10:33 AM, Stephan Koops wrote:

> Hi Marc,
>> One thing we could consider is to make the JAXBContext usage more
>> obvious.
> I have also to say that I need time to understand what the
> ContextResolver is for. You could add some javadoc, that an example
> use is for JAXBContext.
> best regards
> Stephan
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Marc Hadley <marc.hadley at>
CTO Office, Sun Microsystems.