RxExample.java

void fetchTopTrendingList() {
        OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .addNetworkInterceptor(new StethoInterceptor())
                .build();

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(BuildConfig.SERVER_URL)
                .client(okHttpClient)
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .build();

        final HackerNewsInterface hackerNewsInterface = retrofit.create(HackerNewsInterface.class);
        List<Observable<StoryResponse>> storyResponseListObservable = hackerNewsInterface.getTopTrendingList()
                .subscribeOn(Schedulers.io())
                .map(new Function<List<Integer>, List<Observable<StoryResponse>>>() {
                    @Override
                    public List<Observable<StoryResponse>> apply(List<Integer> ids) throws Exception {
                        List<Observable<StoryResponse>> storyResponseListObservable = new ArrayList<>();

                        int listLimit = ids.size() < 10 ? ids.size() : 10;

                        for (int i = 0; i < listLimit; i++) {
                            storyResponseListObservable.add(hackerNewsInterface.getStory(ids.get(i)));
                        }

                        return storyResponseListObservable;
                    }
                }).blockingSingle();

        Observable.zip(storyResponseListObservable, new Function<Object[], List<StoryResponse>>() {
            @Override
            public List<StoryResponse> apply(Object[] objects) throws Exception {
                List<StoryResponse> storyResponseList = new ArrayList<>();

                for (Object object : objects) {
                    if (object instanceof StoryResponse) {
                        storyResponseList.add((StoryResponse) object);
                    }
                }

                return storyResponseList;
            }
        }).subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<List<StoryResponse>>() {
                    @Override
                    public void accept(List<StoryResponse> storyResponses) throws Exception {
                        try {
                            mStoryListView.populateStoryList(storyResponses);
                        } catch (Exception e) {
                            Log.e(TAG, e.getMessage(), e);
                        }
                    }
                });
    }