JAX-RS Content Handlers - RESTful Java with JAX-RS 2.0 - page 94

shaller.isWriteable() implementation. This parameter would be useful, for example, if
we wanted to know the type parameter of a java.util.List generic type.

The third parameter is an array of java.lang.annotation.Annotation objects. These an-
notations are applied to the JAX-RS resource method we are marshalling the response for.
Some MessageBodyWriters may be triggered by JAX-RS resource method annotations
rather than class annotations. In our JAXBMarshaller class, we do not use this parameter in
our isWriteable() implementation.
The fourth parameter is the media type that our JAX-RS resource method wants to produce.

Let's examine the rest of our JAXBMarshaller implementation:

public public long long getSize ( Object obj , Class <?> type , Type genericType ,

Annotation [] annotations , MediaType mediaType )

{

return return − 1 ;

}

The getSize() method is responsible for determining the Content-Length of the response.
If you cannot easily determine the length, just return -1. The underlying HTTP layer (i.e., a
servlet container) will handle populating the Content-Length in this scenario or use the
chunked transfer encoding.

The first parameter of getSize() is the actual object we are outputting. The rest of the para-
meters serve the same purpose as the parameters for the isWriteable() method.

Finally, let's look at how we actually write the JAXB object as XML:

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 = JAXBContext . newInstance ( type );
ctx . createMarshaller (). marshal ( target , outputStream );
} catch catch ( JAXBException ex ) {

throw

throw new new RuntimeException ( ex );

}

}