reactor-core/src/main/java/reactor/core/publisher/Flux.java
public final Flux<T> doOnError(Predicate<? super Throwable> predicate,
			final Consumer<? super Throwable> onError) {
		Objects.requireNonNull(predicate, "predicate");
		return doOnError(t -> {
			if (predicate.test(t)) {
				onError.accept(t);
			}
		});
	}
public final Flux<T> doOnError(Predicate<? super Throwable> predicate,
			final Consumer<? super Throwable> onError) {
		Objects.requireNonNull(predicate, "predicate");
		return doOnError(t -> {
			if (predicate.test(t)) {
				onError.accept(t);
			}
		});
	}
Add behavior (side-effect) triggered when the {@link Flux} completes with an error matching the given exception.
<p>
<img class="marble" src="doc-files/marbles/doOnErrorWithPredicateForFlux.svg" alt="">

@param predicate the matcher for exceptions to handle
@param onError the error handler for each error

@return an observed  {@link Flux}