Retrofit callback wrapper with extra method to indicate the state of the request

Resource.java

package comtas.com.zoolvibs.network;

import javax.annotation.Nullable;

/**
 * Created by m7mdra on 23/12/17.
 */


public interface Resource<T> {
    /**
     * indicate the resource loading
     *
     * @param isLoading true if loading false otherwise
     */
    void onLoading(boolean isLoading);

    /**
     * called when an exception is thrown by the resource
     * @param throwable
     */
    void onError(Throwable throwable);

    /**
     * @param t resource response , it could be null.
     */
    void onSuccess(@Nullable T t);

}

Response.java

package comtas.com.zoolvibs.network;

import android.support.annotation.NonNull;

import okhttp3.Request;
import retrofit2.Call;
import retrofit2.Callback;

/**
 * Created by m7mdra on 24/01/18.
 */

public class Response<T> implements Callback<T> {
    private Resource<T> res;

    private Response(Resource<T> resource) {
        res = resource;
    }

    public static <T> Response<T> create(Resource<T> resource) {
        if (resource == null)
            throw new NullPointerException("Resource interface can not be null");
        final Response<T> response = new Response<>(resource);
        resource.onLoading(true);
        return response;
    }

    public Response<T> start() {
        res.onLoading(true);
        return this;
    }

    @Override
    public void onResponse(@NonNull Call<T> call, @NonNull retrofit2.Response<T> response) {
        res.onLoading(false);
        final T body = response.body();
        //add filtering here here , like http request status 
        //if(response.code()==401){
        //res.onError(new UnauthorizedUserException());
    //    }
       
        res.onSuccess(body);

    }

    @Override
    public void onFailure(@NonNull Call<T> call, @NonNull Throwable t) {
        res.onLoading(false);

        res.onError(t);
    }
}

test.java

  createService(User.class).login(username, password, FirebaseInstanceId.getInstance().getToken()).enqueue(Response.create(new Resource<AuthResponse>() {
            @Override
            public void onLoading(boolean isLoading) {
                    //show loading progress
                if (isLoading)
                    mProgressDialog.show(getFragmentManager(), "");
                else
                    mProgressDialog.dismiss();
            }

            @Override
            public void onError(Throwable throwable) {
                    //handle error here
               if (throwable instanceof IOException)
                //network/json parsing related error.
               else if(throwable instanceof UnauthorizedUserException){
                   startActivity(new Intent(getApplicationContext(),LoginActivity.class))
                   finish();
               }
                //other error
            }

            @Override
            public void onSuccess(@Nullable AuthResponse authResponse) {
                    //on call ended , but its dose not means successful request.
            }
        }));