CODEWITHSUNDEEP
javareactive-programmingspring-webfluxproject-reactor
user471011
user471011

Reputation: 7374

How to throw an exception properly when do Flux processing?

Existing code that I have:

private Flux<Integer> testGetFluxTestData() {
    return Flux.just(new TestData(1), new TestData(2))
            .collectList()
            .map(list -> list.stream()
                    .map(TestData::getId)
                    .collect(Collectors.toList()))
            .flatMapMany(Flux::fromIterable);
}

I want to enrich existing code and throw an exception when some not allowed data received, I made the following changes:

    private Flux<Integer> testGetFluxTestData2() {
        return Flux.just(new TestData(1), new TestData(2))
                .collectList()
                .map(list -> {
                    return !list.contains(new TestData(1)) ?
                            list.stream()
                                    .map(TestData::getId)
                                    .collect(Collectors.toList()) :
                            Flux.error(new IllegalTestDataException("illegal test data 1"));
                })
                .flatMapMany(Flux::fromIterable);
    }

but my implementation even noncompilable due to the following line:

Flux.error(new IllegalTestDataException("illegal test data 1"));

Could you please suggest, how to handle exception throwing for my particular scenario?

Upvotes: 0

Views: 1134

Answers (1)

Simon Basl&#233;
Simon Basl&#233;

Reputation: 28301

You are attempting to map from a List<TestData> to either a List<Integer> or a Flux<?> (error), which makes the desired result type ambiguous. Returning a reactive type in a mapping function is generally not desired (you'd want to do that in a flatmapping function).

(side note: even if you were in a flatMap, it wouldn't work either because at that point you're in Mono API due to collectList, so Mono.flatMap expects a Mono result to the Function).

Note that the map operator catches exceptions from the lambda and turn them into an onError signal, so technically you could replace the Flux.error with a throw.

Otherwise, you'd need to turn the map into a flatMap and the Flux.error into a Mono.error, for the reasons stated above.

Upvotes: 1

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