RxAndroid 기본 2 (Error Handler)

error handling

subscribe 에서 에러 처리

Observable.create(new ObservableOnSubscribe<String>() { @Override public void subscribe(ObservableEmitter<String> subscriber) throws Exception { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); } }).subscribe(new DefaultObserver<String>() { @Override public void onNext(String value) { log("on next: " + value); } @Override public void onError(Throwable e) { // 에러시 처리를 여기로 받음 log("error:" + e); } @Override public void onComplete() { log("completed"); } });

출력결과

subscribe

on next: emit 1

on next: emit 2

error:java.lang.Throwable

람다식으로

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

onError을 정확하게 해주지 않으면 Crash가 발생한다.

Observable.create(new ObservableOnSubscribe<String>() { @Override public void subscribe(ObservableEmitter<String> subscriber) throws Exception { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); } }).subscribe(new Consumer<String>() { @Override public void accept(String s) throws Exception { log("on next: " + s); } });

출력결과

subscribe

on next: emit 1

on next: emit 2

Crash!!

by rx.exceptions.OnErrorNotImplementedException

Error 캐치

onErrorReturn

Observable 체인 안에서 발생한 Error 를 캐치해서, 대체할 Object로 변환하는 것으로 subscriber에 Error가 전달되는 것을 막을 수 있다.

Observable.create(new ObservableOnSubscribe<String>() { @Override public void subscribe(ObservableEmitter<String> subscriber) throws Exception { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); } }).onErrorReturn(new Function<Throwable, String>() { @Override public String apply(Throwable throwable) throws Exception { return "return"; } }).subscribe(new DefaultObserver<String>() { @Override public void onNext(String value) { log("on next: " + value); } @Override public void onError(Throwable e) { // 에러시 처리를 여기로 받음 log("error:" + e); } @Override public void onComplete() { log("completed"); } });

출력결과

subscribe

on next: emit 1

on next: emit 2

on next: return

completed

람다식으로

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).onErrorReturn(throwable -> "return") .subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

OnErrorResumeNext

Observable 체인에서 발생한 Error를 캐치해서, 그 안에서 다시 한 번 Observable를 호출하면 에러시 대체 Stream을 반환할 수 있다.

Observable.create(new ObservableOnSubscribe<String>() { @Override public void subscribe(ObservableEmitter<String> subscriber) throws Exception { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); } }).onErrorResumeNext(new Function<Throwable, ObservableSource<? extends String>>() { @Override public ObservableSource<? extends String> apply(Throwable throwable) throws Exception { return Observable.fromArray(new String[]{"resume 1", "resume 2"}); } }).subscribe(new DefaultObserver<String>() { @Override public void onNext(String value) { log("on next: " + value); } @Override public void onError(Throwable e) { // 에러시 처리를 여기로 받음 log("error:" + e); } @Override public void onComplete() { log("completed"); } });

출력결과

subscribe

on next: emit 1

on next: emit 2

on next: resume 1

on next: resume 2

completed

람다식으로

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).onErrorResumeNext(observer -> {Observable.fromArray(new String[]{"resume 1", "resume 2"});}) .subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

Retry

Error가 일어났을 때, 자동으로 subscribe를 다시 해준다.

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }) .retry() .subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

출력결과

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

.

.

.

성공할때까지 계속... 무한루프 될 가능성이 있으므로 유의해야 한다.

Retry 횟수 제한

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }) .retry(3) .subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

출력결과

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

error:java.lang.Throwable

Retry 좀 더 구체적인 설정

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }) .retry(new BiPredicate<Integer, Throwable>() { @Override public boolean test(Integer integer, Throwable throwable) throws Exception { if (integer < 3) { return true; } return throwable instanceof IllegalStateException; } }) .subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

출력결과

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

error:java.lang.Throwable

람다식으로

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }) .retry((integer, throwable) -> { if (integer < 3) { return true; } return throwable instanceof IllegalStateException; }) .subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

RetryWhen

보다 세밀하게 retry 처리를 제어하기 위한 함수.

Observable.create(subscriber -> { subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).retryWhen(new Function<Observable<Throwable>, ObservableSource<?>>() { @Override public ObservableSource<?> apply(Observable<Throwable> throwableObservable) throws Exception { return throwableObservable.flatMap(new Function<Throwable, ObservableSource<?>>() { @Override public ObservableSource<?> apply(Throwable throwable) throws Exception { return Observable.timer(3, TimeUnit.SECONDS); } }); } }).subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

출력결과

subscribe

on next: emit 1

on next: emit 2

// 3초 후

subscribe

on next: emit 1

on next: emit 2

// 3초 후

subscribe

on next: emit 1

on next: emit 2

.

.

.

반복

람다식으로

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).subscribeOn(AndroidSchedulers.mainThread()) .retryWhen(throwableObservable -> throwableObservable.flatMap( throwable -> Observable.timer(3, TimeUnit.SECONDS) )).subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

그냥 Error인채로 종료

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).subscribeOn(AndroidSchedulers.mainThread()) .retryWhen(throwableObservable -> throwableObservable.flatMap( throwable -> Observable.error(throwable) )).subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

출력결과

subscribe

on next: emit 1

on next: emit 2

error:java.lang.Throwable

(error에 대한 별도의 처리를 하지 않았을 때와 동일한 결과)

Error에 대한 처리를 하지 않고 Complete하기

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).onErrorResumeNext(throwable -> {Observable.empty();}) .subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

출력결과

subscribe

on next: emit 1

on next: emit 2

completed

3번 retry하고 종료

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).retryWhen(throwableObservable -> throwableObservable.take(3)) .subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

출력결과

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

subscribe

on next: emit 1

on next: emit 2

completed

이 경우, 앞의 retry(count) 함수와의 차이는 retry(count)에서는 retry 횟수가 제한에 도달한 후에 error로 종료합니다만, 이 케이스는 completed 에서 종료한다는 점이다.

3초 retry를 3번 하고 종료하기

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).retryWhen(new Function<Observable<Throwable>, ObservableSource<?>>() { @Override public ObservableSource<?> apply(@NonNull Observable<Throwable> throwableObservable) throws Exception { return throwableObservable.take(3).flatMap(new Function<Throwable, ObservableSource<?>>() { @Override public ObservableSource<?> apply(@NonNull Throwable throwable) throws Exception { return Observable.timer(3, TimeUnit.SECONDS); } }); } }).subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

출력결과

subscribe

on next: emit 1

on next: emit 2

// 3초 후

subscribe

on next: emit 1

on next: emit 2

// 3초 후

subscribe

on next: emit 1

on next: emit 2

completed

람다식으로

Observable.create(subscriber -> { log("subscribe"); subscriber.onNext("emit 1"); subscriber.onNext("emit 2"); subscriber.onError(new Throwable()); }).retryWhen(throwableObservable -> throwableObservable.take(3).flatMap( throwable -> Observable.timer(3, TimeUnit.SECONDS) )).subscribe(s -> log("on next: " + s) , e -> log("error:" + e) , () -> log("completed"));

에러 핸들러를 구독하고 제공하는지 항상 확인해야 합니다. 그렇지 않으면 특히 스케줄러를 적용할 때 스택 트레이스에 아무것도 없을 수 있습니다. 물론 RxJava 절에서 뭔가 잘못됐다고 알려주긴 하지만 어디서 발생했는지 찾을 방법이 없습니다. 항상 에러 콜백을 사용하고, 에러가 발생한다면 에러를 로그로 남겨서 예상치 못한 오류를 기록해야 합니다.

RxLint : https://bitbucket.org/littlerobots/rxlint

참고자료

http://pluu.github.io/blog/rxjava/2015/12/11/rxjava-error/

http://realignist.me/code/2016/05/29/rxjava-on-android.html

http://blog.danlew.net/2015/12/08/error-handling-in-rxjava/

https://realm.io/kr/news/mobilization-hugo-visser-rxjava-for-rest-of-us/