Use Fallback Observable x number of times

Question

I have an Observable which implements Error handling in the onErrorResumeNext method.

getMyObservable(params)
                .take(1)
                .doOnError(e -> {
                })
                .onErrorResumeNext(throwable -> {
                    if (throwable.getMessage().contains("401")) {
                        return getMyObservable(params);
                    } else {
                        sendServerCommunicationError();
                        return Observable.error(throwable);
                    }
                })
                .subscribe(result -> {
                             ...                                }
                });

GetMyObservable() returns a web service request from a generated client. The Use Case is: If we receive 401 we may need to refresh the client with a new UserToken. That is why we use the Fallback Observable in onErrorResumeNext() and cannot just use retry.

I have some questions:

1. Why do I need to implement doOnError? If I don´t implement it, I sometimes get an "onError not implemented" Exception. I thought when I use onErrorResumeNext, this method is automatically used in case of an Error.
2. How can I achieve that on specific Errors (like 401) I use a fallback Observable with some backoff time and after 5 Times I produce an Error. So can I combine retryWhen and onErrorResumeNext somehow or is it done differently?

Answer 1

Why do I need to implement doOnError?

You don't and doOnError is not an error handler but a peek into the error channel. You have to implement an error handler in subscribe:

.subscribe(result -> {
    // ...
},
error -> {
    // ...
});

How can I achieve that on specific Errors (like 401) I use a fallback Observable with some backoff time and after 5 Times

Use retryWhen:

Observable.defer(() -> getMyObservable(params))
.retryWhen(errors -> {
    AtomicInteger count = new AtomicInteger();
    return errors.flatMap(error -> {
       if (error.toString().contains("401")) {
           int c = count.incrementAndGet();
           if (c <= 5) {
               return Observable.timer(c, TimeUnit.SECONDS);
           }
           return Observable.error(new Exception("Failed after 5 retries"));
       }
       return Observable.error(error);
    })
})