retry chaining with onErrorReturnItem rxJava - rx-java2

Question

I have create one observable
Observable<Map<Integer, String>> observable = Observable.create(s -> {
try {
System.out.println("getMultipleCitiesName ==="+Thread.currentThread().getName());
List<String> cityIdsString = new ArrayList<>();
for (Integer cityId : cityIds) {
cityIdsString.add(cityId.toString());
}
MultiValueMap<String, String> formParams = new LinkedMultiValueMap<>();
formParams.put("cityIds[]", cityIdsString);
// Call the Location Client to call the API
Response<Map<Integer, String>> response = locationClient.getMultipleCitiesName(formParams);
s.onNext(response.getData());
} catch (Exception e) {
System.out.println("Inside Exception CITY NEW");
s.onError(e);
}
s.onComplete();
});
Now I want to add onErrorReturnItem() and retry() both.
So I tried it two ways
a) observable = observable.onErrorReturnItem(new HashMap<>()).retry(3);
b) observable = observable.retry(3).onErrorReturnItem(new HashMap<>());
b) is working (meaning retry and onErrorReturnItem) both are working
while in a) retry is not working?
Why is that

Answer 1

Order of operators matters, this is how you have to interpret the chains:
(a) you're saying something like Let take whatever comes from observable and if some error happens upstream then let have an observable that emit an empty HashMap(i.e calling onErrorReturnItem) and then retry on this observable(if some error is emitted). but no error is emitted by the observable onErrorReturnItem it just emit the empty HashMap followed by an onComplete signal. i.e whatever the error happens upstream is hidden by onErrorReturnItem and retry would never be signaled an onError to start retrying.
(b) you've saying completely the opposite, Let take whatever comes from observable and if some error happens upstream let retry, if retry can't get any valid item after 3 attempts, then signal onError downstream and onErrorReturnItem will return an empty HashMap.
Now it should be clear why (b) tend be what you're expecting to happens.