public class RSSProducerResource extends AbstractResource {

	@Override
	protected ResourceResponse newResourceResponse(Attributes attributes) {
		ResourceResponse resourceResponse = new ResourceResponse();
		resourceResponse.setContentType("text/xml");
		resourceResponse.setTextEncoding("utf-8");
		
		resourceResponse.setWriteCallback(new WriteCallback()
		{
			@Override
			public void writeData(Attributes attributes) throws IOException
			{
				OutputStream outputStream = attributes.getResponse().getOutputStream();
				Writer writer = new OutputStreamWriter(outputStream);
				SyndFeedOutput output = new SyndFeedOutput();
		        try {
					output.output(getFeed(), writer);
				} catch (FeedException e) {
					throw new WicketRuntimeException("Problems writing feed to response...");
				}
			}			
		});
		
		return resourceResponse;
	}
	
	//method getFeed() 
}

Method newResourceResponse returns an instance of ResourceResponse representing the response generated by the custom resource. Since RSS feed is basically a XML fragment, in the code above we have set the type of the response to text/xml and the text encoding to utf-8.

To specify the content that will be returned by our resource we must also provide an implementation of inner class WriteCallback, which is responsible for writing content data to response's output stream. In our project we used class SyndFeedOutput from Rome framework to write our feed to response. Method getFeed() is just an utility method that generates a sample RSS feed (which is an instance of standard interface com.sun.syndication.feed.synd.SyndFeed).

Now that we have our custom resource in place, we can use it in our applications. Class WebApplication provides method mountResource which can be used to mount a given resource to a specific path:

public class WicketApplication extends WebApplication
{    		
	@Override
	public void init()
	{
		super.init();
		ResourceReference resourceReference = new ResourceReference("rssProducer"){
			RSSProducerResource deviceMetaResource = new RSSProducerResource();
			@Override
			public IResource getResource() {
				return deviceMetaResource;
			}};
			
		mountResource("/foo/bar", resourceReference);				
	}
}

@Test
public void testMountedResourceResponse() throws IOException, FeedException
{
	tester.startResource(new RSSProducerResource());
	String responseTxt = tester.getLastResponse().getDocument();
	//write the RSS feed used in the test into a ByteArrayOutputStream
	ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
	Writer writer = new OutputStreamWriter(outputStream);
	SyndFeedOutput output = new SyndFeedOutput();
       	
	output.output(RSSProducerResource.getFeed(), writer);
	//the response and the written RSS must be equal 
	Assert.assertEquals(responseTxt, outputStream.toString());
}