JAX-RS Content Handlers - RESTful Java with JAX-RS 2.0 - page 97

< T extends extends Throwable > ExceptionMapper < T >

getExceptionMapper ( Class < T > type );

}

We use the Providers.getContextResolver() method to find a ContextResolver . We in-
ject a reference to a Providers object using the @Context annotation. Let's modify our
JAXBMarshaller class to add this new functionality:

@Context
protected Providers providers ;

public public void void writeTo ( Object target ,

Class <?> type ,
Type genericType ,
Annotation [] annotations ,
MediaType mediaType ,
MultivaluedMap < String , Object > httpHeaders ,
OutputStream outputStream ) throws

throws IOException

{

try try {

JAXBContext ctx = null

null ;
ContextResolver < JAXBContext > resolver =
providers . getContextResolver ( JAXBContext . class , mediaType );
iif ( resolver != null null ) {

ctx = resolver . getContext ( type );

}
iif ( ctx == null null ) {

// create one ourselves
ctx = JAXBContext . newInstance ( type );

}
ctx . createMarshaller (). marshal ( target , outputStream );
} catch catch ( JAXBException ex ) {

throw

throw new new RuntimeException ( ex );

}

}

In our writeTo() method, we now use the Providers interface to find a ContextResolver
that can give us a custom JAXBContext . If one exists, we call resolver.getContext() ,
passing in the type of the object we want a JAXBContext for.

The ContextResolver returned by Providers.getContextResolver() is actually a proxy
that sits in front of a list of ContextResolvers that can provide JAXBContext instances.
When getContextResolver() is invoked, the proxy iterates on this list, recalling getCon-