rxjava_zip_sample.java

        Maybe<List<Long>> maybe = Maybe
                .zip(
                        webViewRepository.getHabitReadArticle(webView),
                        habitReadArticleDao.getAll(),
                    new BiFunction<HabitReadArticleWebViewLocal, List<HabitReadArticle>, List<Long>>() {
                        @Override
                        public List<Long> apply(HabitReadArticleWebViewLocal habitReadArticleWebViewLocal, List<HabitReadArticle> habitReadArticles) throws Exception {
                            if (!hasSameArticleIds(habitReadArticleWebViewLocal, habitReadArticles)) {
                                return saveArticles(habitReadArticleWebViewLocal);
                            }
                            return null;
                        }
                    }
                )
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread());

        disposables.add(maybe.subscribeWith(new ImportWebViewLocalObserver()));