Late Subscribing and Polling with ReactiveX (http://blog.grio.com/2016/01/rxandroid-polling-and-other.html)

DataService.java

ConnectableObservable<Wrapper<List<Data>>> dataObservable;

public Observable<Wrapper<List<Data>>> getData() {
   if (dataObservable == null) {
       dataObservable = webService.getApiData()
               .compose((Observable.Transformer<List<Data>, List<Data>>) networkScheduling)
               .map(dataList -> Wrapper.response(dataList))
               // Retry a few times before letting an error through.
               .retry(5) 
               .onErrorResumeNext(throwable -> {
                   // If the server is unreachable, let the subscriber know.
                   // The user may be able to do something about his connection.
                   if (throwable instanceof UnknownHostException || throwable instanceof ...) {
                       // Recoverable error - transmit error without breaking.
                       return Observable.just(Wrapper.error(throwable));
                   }
                   // In case of an unrecoverable error, let it end.
                   return Observable.error(throwable); 
               })
               .repeatWhen(observable ->
                       Observable.interval(5, TimeUnit.MINUTES)
                           .mergeWith(hook)
               )
               .replay(1);

       dataObservable.connect();
   }
   return dataObservable;
}

public void triggerDataFetch() {
   hook.onNext(-1L);
}

Observable.Transformer networkScheduling = observable ->
       observable.subscribeOn(Schedulers.io())
               .unsubscribeOn(Schedulers.io())
               .observeOn(AndroidSchedulers.mainThread());
 
// Consumer
dataService.getData().
       subscribe(wrapper -> {
           if (wrapper.hasError()) {
               // handle error
           } else {
               List<Data> list = wrapper.response;
               // do something.
           }
       }, e -> logger.error("Unrecoverable error getting data.", e));


public interface Webservice {
   @GET("api/data")
   public Observable<List<Data>> getApiData();
}

public static class Wrapper<ResponseType> {
   public Throwable error;
   public ResponseType response;

   private Wrapper() { }

   public static <T> Wrapper<T> error(Throwable t) {
       Wrapper<T> wrapper = new Wrapper<T>();
       wrapper.error = t;
       return wrapper;
   }

   public static <T> Wrapper<T> response(T response) {
       Wrapper<T> wrapper = new Wrapper<T>();
       wrapper.response = response;
       return wrapper;
   }

   public boolean hasError() { return error != null; }
}