Issue
If I use switchIfEmpty for a Mono for example, I have a hard time locating where the actual comparison (if the Mono is in fact empty) is happening. The first thing my IDE jumps to, is the snippet below.
public final Mono<T> switchIfEmpty(Mono<? extends T> alternate) {
return onAssembly(new MonoSwitchIfEmpty(this, alternate));
}
However, onAssembly only calls a static method / value in the Hooks abstract class. That hook "onEachOperatorHook" does seem to use an Functional Interface, but I can't seem to find where this is placed / coded.
The comments also mention pointcuts, but I also don't find any hints into any @Aspect annotated classes, so I assume it's implemented with the Hooks only.
Can anyone point me in the right direction, where the Hooks actually take the information from (supposedly a Lambda) for comparing the two Monos in case of switchIfEmpty?
Many thanks.
Solution
The logic is taking place inside SwitchIfEmptySubscriber<T>
:
static final class SwitchIfEmptySubscriber<T> extends Operators.MultiSubscriptionSubscriber<T, T> {
final Publisher<? extends T> other;
boolean once;
SwitchIfEmptySubscriber(CoreSubscriber<? super T> actual, Publisher<? extends T> other) {
super(actual);
this.other = other;
}
public void onNext(T t) {
if (!this.once) {
this.once = true;
}
this.actual.onNext(t);
}
public void onComplete() {
if (!this.once) {
this.once = true;
this.other.subscribe(this);
} else {
this.actual.onComplete();
}
}
public Object scanUnsafe(Scannable.Attr key) {
return key == Attr.RUN_STYLE ? RunStyle.SYNC : super.scanUnsafe(key);
}
}
In case of an empty Mono:
onComplete()
is triggeredthis.once
is false sinceonNext()
has not been executedthis.other
publisher (the alternativeMono
given inswitchIfEmpty
) gets subscribed
Answered By - lkatiforis
Answer Checked By - Willingham (JavaFixing Volunteer)