Restlete Client :: how to add filters?

I am suffering from a lack of documentation on using Restlet on the client side. I am getting the resource on the server via ClientResource:

new ClientResource(url).get();

      

        
        
        
      

    

But the server can return an ETag header. To handle this, I want to save the ETag on checkout and send it back to the server using the same url. I am currently doing it like this:

ClientResource clientResource = new ClientResource(url);
addEtag(url, clientResource); // add the cached ETag to the query if any
clientResource.get();
saveEtag(url, clientResource); // cache the ETag if any

      

        
        
        
      

    

I would like to do this using the Restlet environment. I search for days without understanding the missing link. I can extend the application, overwrite the createOutboundRoot () method and return the filter:

public class RestLetClient extends Application {

    private Client client;

    // instantiation of the client and other things here

    @Override
    public Restlet createOutboundRoot() {
        return new Filter(getContext(), client){

            @Override
            protected int beforeHandle(Request request, Response response) {
                addEtag(request);
                return super.doHandle(request, response);
            }

            @Override
            protected void afterHandle(Request request, Response response) {
                saveEtag(request, reponse);
                return super.afterHandle(request, response);
            }
        };
    }
}

      

        
        
        
      

    

BUT how can I use this filtering around the Restlet client from my business code?

EDIT

The best I could work so far is:

Request request = new Request(Method.GET, uri);
//the filter created in original post
filter.handle(request).getEntity();

      

        
        
        
      

    

It works, but it is not integrated into the framework. What I intend to do is on the client side what is only documented for the server side. On the server, you will do:

public class ServerApplication extends Application {

    @Override
    public Restlet createInboundRoot() {
        Router router = new Router(getContext());
        router.attach(GET_URL, GetResource.class);
        return router;
    }
}

      

        
        
        
      

    

and then start the server. The application will be initiated when it receives a GET request for a URL.
What is the client side equivalent? How can I call the client application? If I have an application running on the client side, I can add filters where they belong to the REST application.

EDIT 2

When trying to run my client in my application, I get the error: The filter org.restlet.engine.application.RangeFilter@f372a7a was executed without the following Restlet attached to it.

This is how I get the error. I have a class extension that is called from a JUnit test:

public class RestLetClient extends Application {

    private final Client client;

    Logger logger = LoggerFactory.getLogger(getClass());

    public RestLetClient() {
        this.client = new Client(Protocol.HTTP);
    }

    public Representation get(final String uri) throws Exception {

        Request request = new Request(Method.GET, uri);
        Response response = handle(request);
        return response.getEntity();
    }

    @Override
    public Restlet createOutboundRoot() {
        return new Filter(getContext(), client) {
            @Override
            protected int beforeHandle(Request request, Response response) {
                addEtagFilter(request);
                return super.beforeHandle(request, response);
            }

            @Override
            protected void afterHandle(Request request, Response response) {
                saveEtagFilter(request, response);
                super.afterHandle(request, response);
            }
        };
    }

    private void saveEtagFilter(Request request, Response response) {
        logger.debug("saving etag");
    }

    private void addEtagFilter(Request request) {
        logger.debug("adding etag");
    }
}

      

        
        
        
      

    

and a device with one test method:

public class RestLetClientTest {

    public static final String URL = "http://localhost:8123/resource";

    private RestLetClient instance;

    private Server server;

    @Before
    public void setUp() throws Exception {
        server = new Server(Protocol.HTTP, 8123, new TestApplication());

        server.start();

        instance = new RestLetClient();
        instance.start();
    }

    @After
    public void tearDown() throws Exception {
        instance.stop();
    }

    @Test
    public void testGet() throws Exception {
        Representation representation = instance.get(URL);
        System.out.println(representation.getText());
    }

    private class TestApplication extends Application {
        @Override
        public Restlet createInboundRoot() {
            return new Router().attach(RestLetClientTest.URL, GetResource.class);
        }
    }

    private class GetResource extends ServerResource {
        @Get
        public Representation getResource() {
            return new StringRepresentation("hello world");
        }
    }
}

      

        
        
        
      

    

What am I doing wrong?