How to continue streaming items after error in RxJ

问题:

I'm RxJava newbie, and I've got following problem. Say I have sequence of items and on of items propagates error, I want to ignore it and to continue processing other items.

I have following snippet:

    Observable.from(Arrays.asList("1", "2", "3"))
            .map(x -> {
                if (x.equals("2")) {
                    throw new NullPointerException();
                }
                return x + "-";
            })
            .onExceptionResumeNext(Observable.empty())
            .subscribe(System.out::println);

I'm getting: 1-

But I want to get: 1- , 3-

How can I do that?

回答1:

the trick is to wrap the value, which would be transformed somehow, into a new observable and flatmap over it as in the following example. Each value in the flatMap can now throw a exception and handle it value by value. Becuase the substream in flatMap consists only of one element, it does not matter if the observable will be closed after onError. I use RxJava2 as test-environment.

@Test
public void name() throws Exception {
    Observable<String> stringObservable = Observable.fromArray("1", "2", "3")
            .flatMap(x -> {
                return Observable.defer(() -> {
                    try {
                        if (x.equals("2")) {
                            throw new NullPointerException();
                        }
                        return Observable.just(x + "-");
                    } catch (Exception ex) {
                        return Observable.error(ex);
                    }
                }).map(s -> {
                    if (s.equals("3-")) {
                        throw new IllegalArgumentException();
                    }
                    return s + s;
                }).take(1)
                        .zipWith(Observable.just("X"), (s, s2) -> s + s2)
                        .onErrorResumeNext(Observable.empty());
            });

    TestObserver<String> test = stringObservable.test();

    test.assertResult("1-1-X");
}