RxJava: how to unsubscribe a subject from an observable

Question

Using RxJava3, given an Observable and a Subject, I can subscribe the Subject to the Observable:

observable.subscribe(subject); // returns void, not a subscription

Later, my Subject is not interested anymore in the Observable, how to unsubscribe it from the Observable ?

Answer 1

I think the simplest option is to use an overload of subscribe that returns a Disposable, and have each handler call the appropriate method on your Subject, like this:

Disposable d = observable
    .subscribe(subject::onNext, subject::onError, subject::onComplete);

// Later
d.dispose();

You could also create a DisposableObserver that forwards all messages to the Subject, and use subscribeWith instead of subscribe, though it's more verbose:

Disposable d = observable
.subscribeWith(new DisposableObserver<Integer>() {
         @Override public void onStart() {
         }
         @Override public void onNext(Integer t) {
             subject.onNext(t);
         }
         @Override public void onError(Throwable t) {
             subject.onError(t);
         }
         @Override public void onComplete() {
             subject.onComplete();
         }
     });

I'm not aware of any cleaner options, and this issue from the RxJava bug tracker seems to back that up, though it is targeted at RxJava2.