public Observable<String> getMyString(String key){
        WebRequestDbEntity myCachedString = mCache.getWebRequest(key);
        String cachedString = myCachedString.getValue();

        return retrofitWebDataStore().getMyString(key)
                .startWith(Observable.just(cachedString))
                .map(networkString -> {
                    mCache.saveRequest(key, networkString);
                    return networkString;
                });
    }

getNeworkString(key)
                    .subscribeOn(Schedulers.io())
                    .observeOn(AndroidSchedulers.mainThread())
                    .subscribe(this::onSuccess, this::onError);