How to handle error while executing Flux.map()

Question

I´m trying to figure out how handle errors when mapping elements inside a Flux.

For instance, I´m parsing a CSV string into one of my business POJOs:

myflux.map(stock -> converter.convertHistoricalCSVToStockQuotation(stock)); 

Some of this lines might contain errors, so what I get in the log is:

 reactor.core.publisher.FluxLog:  onNext([SOME_BOGUS_QUOTE]@38.09 (Fri Apr 08 00:00:00 CEST 2016) H(38.419998)/L(37.849998)/O(37.970001))  reactor.core.publisher.FluxLog:  onNext([SOME_BOGUS_QUOTE]@38.130001 (Thu Apr 07 00:00:00 CEST 2016) H(38.189999)/L(37.610001)/O(37.799999))  reactor.core.publisher.FluxLog:  onError(java.lang.IllegalArgumentException: Invalid CSV stock quotation: SOME_BOGUS_QUOTE,trololo)  reactor.core.publisher.FluxLog:  java.lang.IllegalArgumentException: Invalid CSV stock quotation: SOME_BOGUS_QUOTE,trololo 

I read in the API some error handling methods, but most refered to returning an "error value" or using a fallback Flux, like this one:

Flux.onErrorResumeWith(myflux, x -> Mono.fromCallable(() -> ... do stuff); 

However, using this with my myflux means that the whole flux is processed again.

So, is there a way to handle errors while processing particular elements (I.e ignoring them/Logging them) and keep processing the rest of the flux?

UPDATE with @akarnokd workaround

public Flux<StockQuotation> getQuotes(List<String> tickers) {     Flux<StockQuotation> processingFlux = Flux.fromIterable(tickers)     // Get each set of quotes in a separate thread     .flatMap(s -> Mono.fromCallable(() -> feeder.getCSVQuotes(s)))     // Convert each list of raw quotes string in a new Flux<String>     .flatMap(list -> Flux.fromIterable(list))     // Convert the string to POJOs     .flatMap(x -> {             try {                 return Flux.just(converter.convertHistoricalCSVToStockQuotation(x));                 }             catch (IllegalArgumentException ex){                 System.out.println("Error decoding stock quotation: " + x);                 return Flux.empty();             }     });      return processingFlux; } 

This works as a charm, however, as you can see the code is less elegant than before. Does not the Flux API have any method to do what this code does?

retry(...) retryWhen(...) onErrorResumeWith(...) onErrorReturn(...) 

Answer 1

You need flatMap instead which let's you return an empty sequence if the processing failed:

myflux.flatMap(v -> {     try {         return Flux.just(converter.convertHistoricalCSVToStockQuotation(stock));     } catch (IllegalArgumentException ex) {         return Flux.empty();     } }); 

Answer 2

If you want to use Reactor 3's methods for dealing with exceptions, you can use Mono.fromCallable.

flatMap(x ->      Mono.fromCallable(() -> converter.convertHistoricalCSVToStockQuotation(x))         .flux()         .flatMap(Flux::fromIterable)         .onErrorResume(Flux::empty) ) 

Unfortunately there is no Flux.fromCallable, so assuming the callable returns a list, you have to convert it to a Flux manually.