Best way to call serial , batch wise requests in Rx Java - rx-android

Question

I'm new to RxJava. Currently, I'm trying out samples and converting existing codes to Rx.
I have an existing API, which takes a large list of objects,
since server takes time to process a large number of inputs and also due to timeout issues I'm sending inputs to the API in batch wise. if I have 300 objects, I will pass it as batches of 10 objects. As in, first I call the API with first 10 items, waiting for the response, once I received the response, I will take the next 10, till I reach 300 items. Righ now I am using so many nested callbacks and flags to keep track of items and results. I need to convert it to Rx Java.
I tried something with buffer operator and its working as expected. Just wanted to know is there any better solution or is this the exact way to do. My code is given below.
Observable.range(1, 300)
.buffer(10)
.flatMap((integers) -> mockServerResult(integers))
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new DisposableObserver<String>() {
#Override
public void onNext(#NonNull String s) {
Log.d(TAG, "onNext: " + s);
}
#Override
public void onError(#NonNull Throwable e) {
}
#Override
public void onComplete() {
}
});
}
public Observable<String> mockServerResult(List<Integer> integers) {
StringBuilder stringBuilder = new StringBuilder("server Results for ");
for (Integer integer : integers) {
stringBuilder.append(integer.toString()).append(",");
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return Observable.just(stringBuilder.toString());
}