2018년 4월 22일 드로이드 나이츠 2108에서 발표한 RxJava 세션 프리젠테이션입니다.

1. 다시 보는 RxJava
네이버 노재춘

2. Rx Contract #1-1
no more messages should arrive after an onError or
onComplete message
RxView.clicks(button)
.flatMap(ignored -> getBestSeller()
.subscribeOn(Schedulers.io()))
.observeOn(AndroidSchedulers.mainThread())
.subscribe(bookTitle -> title.setText(bookTitle),
e -> Toast.makeText(this, "문제 발생",
Toast.LENGTH_LONG).show()
);
무한 이벤트에서 문제 발생 가능

3. Rx Contract #1-2
RxView.clicks(button)
.flatMap(ignored -> getBestSeller()
.subscribeOn(Schedulers.io())
.map(title -> new ViewState.Result(title)) // (1)
.cast(ViewState.class) // (2)
.onErrorReturn(e -> new ViewState.Error(e))) // (3)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(viewState -> {
if (viewState instanceof ViewState.Result) { // (4)
title.setText(((ViewState.Result) viewState).title);
} else if (viewState instanceof ViewState.Error) { // (5)
Toast.makeText(this, "문제 발생", Toast.LENGTH_LONG).show();
}
});

4. Rx Contract #1-3
interface ViewState {
class Error implements ViewState {
Throwable e;
Error(Throwable e) {
this.e = e;
}
}
class Result implements ViewState {
String title;
Result(String title) {
this.title = title;
}
}
}
http://hannesdorfmann.com/android/
mosby3-mvi-1
visual bugs such as displaying a loading
indicator (“loading state”) and error indicator
(“error state”) at the same time => exactly
one output

5. Rx Contract #2-1
스트림에 널(null) 허용 안됨
@Test(expected = NullPointerException.class)
public void nullEvent() {
Observable.just("Hello", null, "RxJava")
.subscribe(System.out::println,
System.err::println);
}
Observable 생성
에서 에러 발생

6. Rx Contract #2-2
@Test
public void nullEventOnCreate() {
Observable.create(emitter -> {
emitter.onNext("Hello");
emitter.onNext(null);
emitter.onNext("RxJava");
}).subscribe(System.out::println,
System.err::println);
}
java.lang.NullPointerException:
onNext called with null. Null
values are generally not
allowed in 2.x operators and
sources.

7. Rx Contract #2-3
@Test
public void nullEventPossible() {
Observable.just(1, 2, -1, 1, 2)
.map(dollar -> getCurrentPrice(dollar))
.subscribe(System.out::println,
System.err::println);
}
private String getCurrentPrice(int dollar) {
if (dollar < 0) {
return null;
}
return (dollar * 1000) + " won";
}
1000 won
2000 won
java.lang.NullPointerException:
The mapper function returned
a null value.

8. Rx Contract #2-4
@Test
public void nullEventPossible3() {
Observable.just(1, 2, -1, 1, 2)
.map(dollar -> getCurrentPrice3(dollar))
.onErrorReturnItem("0 won")
.subscribe(System.out::println,
System.err::println,
() -> System.out.println("onComplete"));
}
private String getCurrentPrice3(int dollar) {
if (dollar < 0) {
throw new IllegalArgumentException("dollar should be bigger than 0");
}
return (dollar * 1000) + " won";
} [1000 won, 2000 won, 0 won, onComplete]

9. Rx Contract #2-5
@Test
public void nullEventPossible4() {
Observable.just(1, 2, -1, 1, 2)
.flatMap(dollar -> getCurrentPrice4(dollar)
.onErrorReturnItem("0 won")) // (1)
.subscribe(System.out::println,
System.err::println);
}
private Observable getCurrentPrice4(int dollar) {
if (dollar < 0) {
return Observable.error(
new IllegalArgumentException("dollar should be bigger than 0")); // (2)
}
return Observable.just((dollar * 1000) + " won"); // (3)
}

10. Rx Contract #3-1
Assume observer instances are called in a serialized fashion
Observable obs = Observable.create(emitter -> {
new Thread(() -> {
emitter.onNext(1);
emitter.onNext(3);
. . . .
emitter.onNext(9);
// emitter.onComplete(); // (1)
}).start();
new Thread(() -> {
emitter.onNext(2);
emitter.onNext(4);
. . . .
emitter.onNext(10);
// emitter.onComplete(); // (2)
}).start();
});
onComplete 넣
을 수 없음

11. Rx Contract #3-2
obs.subscribe(value -> System.out.println(
Thread.currentThread().getName() + ":" + value),
System.err::println,
() -> System.out.println("onComplete"));
onComplete 불
리지 않음

12. Rx Contract #3-3
Observable obs1 = Observable.create(emitter -> {
new Thread(() -> {
emitter.onNext(1);
. . . .
emitter.onNext(9);
emitter.onComplete(); // (1)
}).start();
});
Observable obs2 = Observable.create(emitter -> {
new Thread(() -> {
emitter.onNext(2);
. . . .
emitter.onNext(10);
emitter.onComplete(); // (2)
}).start();
});
(1), (2)
모두 필요

13. Rx Contract #3-4
Observable.merge(obs1, obs2).subscribe(value ->
System.out.println(Thread.currentThread().getName() + ":" + value),
System.err::println,
() -> System.out.println("onComplete")
);
onComplete 정
상 호출

14. Rx Contract #3-5
Observable obs1 = Observable.create(emitter -> {
emitter.onNext(1);
emitter.onNext(3);
. . . .
emitter.onNext(9);
emitter.onComplete();
}).subscribeOn(Schedulers.computation());
Observable obs2 = Observable.create(emitter -> {
emitter.onNext(2);
emitter.onNext(4);
. . . .
emitter.onNext(10);
emitter.onComplete();
}).subscribeOn(Schedulers.computation());

15. Rx Contract #3-6
Observable.merge(obs1, obs2).subscribe(value ->
System.out.println(
Thread.currentThread().getName() + ":" + value),
System.err::println,
() -> System.out.println("onComplete")
);

16. flatMap thread #1-1
repository.getBookCategories().toObservable()
.flatMapIterable(categories -> categories)
.flatMapSingle(category -> repository.getCategoryBooks(category.categoryId))
.subscribeOn(Schedulers.io())
.collect(ArrayList::new, ArrayList::addAll)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(books -> title.setText(books.toString()
repository.getBookCategories().toObservable()
.subscribeOn(Schedulers.io())
.flatMapIterable(categories -> categories)
.flatMapSingle(category ->
repository.getCategoryBooks(category.categoryId)
.subscribeOn(Schedulers.io()))
.collect(ArrayList::new, ArrayList::addAll)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(books -> title.setText(books.toString()));

17. flatMap thread #1-2

18. flatMap thread #2 단일 이벤트 연결
repository.getRegion(location)
.map(region -> region.areaCode)
.flatMap(repository::getWeather)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(weather -> title.setText(weather.toString()));
repository.getRegion(location)
.subscribeOn(Schedulers.io())
.map(region -> region.areaCode)
.flatMap(areaCode -> repository.getWeather(areaCode)
.subscribeOn(Schedulers.io()))
.observeOn(AndroidSchedulers.mainThread())
.subscribe(weather -> title.setText(weather.toString()));

19. merge thread #1-1
Single.merge(repository.getBestSeller(),
repository.getRecommendBooks(),
repository.getCategoryBooks(7))
.subscribeOn(Schedulers.io())
.collect(ArrayList::new, ArrayList::addAll)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(books -> title.setText(books.toString()));
Single.merge(repository.getBestSeller().subscribeOn(Schedulers.io()),
repository.getRecommendBooks().subscribeOn(Schedulers.io()),
repository.getCategoryBooks(7).subscribeOn(Schedulers.io()))
.collect(ArrayList::new, ArrayList::addAll)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(books -> title.setText(books.toString()));

20. merge thread #1-2

21. zip thread #1-1
Single.zip(repository.getWeather(regionCode),
repository.getWeatherDetail(regionCode),
Pair::new)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(pair -> title.setText(pair.first + ", " + pair.second));
Single.zip(repository.getWeather(regionCode).subscribeOn(Schedulers.io()),
repository.getWeatherDetail(regionCode).subscribeOn(Schedulers.io()),
Pair::new)
.observeOn(AndroidSchedulers.mainThread())
.subscribe(pair -> title.setText(pair.first + ", " + pair.second));

22. zip thread #1-2

23. RetryWhen #1
- SocketTimeout에 재시도(3번 재시도)
- 401 status code에는 인증 API 호출

24. RetryWhen #2
public Single<Profile> getProfile() {
return profileRepository.getProfile().retryWhen(errors ->
errors.zipWith(Flowable.range(0, LIMIT),
this::handleRetryAttempt).flatMap(x -> x));
}
private Flowable<Long> handleRetryAttempt(Throwable throwable, int attempt) {
if (throwable instanceof SocketTimeoutException) {
switch (attempt) {
case LIMIT:
return Flowable.error(throwable);
default:
return Flowable.timer(attempt * 3, TimeUnit.SECONDS);
}
} else {else if (throwable instanceof HttpException) {
// 다음 슬라이드
}
OkHttpClient Interceptor도 가능?
원래 흐름으로 돌아올 방법 없음

25. RetryWhen #3
private Flowable<Long> handleRetryAttempt(Throwable throwable, int attempt) {
if (throwable instanceof SocketTimeoutException) {
...
} else if (throwable instanceof HttpException) {
int statusCode = ((HttpException) throwable).code();
if (statusCode == 401) {
return profileRepository.refresh().retry((refreshAttempt, e) ->
refreshAttempt < LIMIT
&& e instanceof SocketTimeoutException)
.map(x -> 1L).toFlowable();
}
}
return Flowable.error(throwable);
}

26. RetryWhen #4
public class RetryTransformer<T> implements SingleTransformer<T, T> {
. . . .
@Override
public SingleSource apply(Single<T> upstream) {
return upstream.retryWhen(errors ->
errors.zipWith(Flowable.range(0, LIMIT),
this::handleRetryAttempt).flatMap(x -> x));
}
}
public Single<Profile> getProfile() {
return profileRepository.getProfile().compose(retryTransformer);
}

27. 예외 처리 #1
public long getTimeInMillis1(String input) throws ParseException {
SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT);
return sdf.parse(input).getTime();
}
public long getTimeInMillis2(String input) {
SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT);
try {
return sdf.parse(input).getTime();
} catch (ParseException e) {
e.printStackTrace();
return -1L; // -1을 상수로 해도 큰 차이가 없음
}
}

28. 예외 처리 #2
public long getTimeInMillis3(String input) {
SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT);
try {
return sdf.parse(input).getTime();
} catch (ParseException e) {
throw new IllegalArgumentException("Illegal input pattern");
}
}

29. 예외 처리 #3
public Single<Long> getTimeInMillis(String input) {
return Single.fromCallable(() -> {
SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT);
return sdf.parse(input).getTime();
});
}
String input = "2017-xx-30 02:20:20";
DateFormatter formatter = new DateFormatter();
long start = formatter.getTimeInMillis(input)
.onErrorReturnItem(0L)
.blockingGet();
long end = formatter.getTimeInMillis(input)
.onErrorReturnItem(new Date().getTime())
.blockingGet();
System.out.println("start=" + start + ", end=" + end);

30. flatMap BiFunction
Observable.range(2, 8)
.flatMap(row -> Observable.range(1, 9)
.map(col -> String.format("%d x %d = %d",
row, col, row * col)))
.subscribe(System.out::println);
Observable.range(2, 8)
.flatMap(row -> Observable.range(1, 9),
(row, col) -> String.format("%d x %d = %d",
row, col, row * col))
.subscribe(System.out::println);

31. collect
Observable<String> obs = Observable.fromIterable(searchOptions)
.filter(SearchOption::isInUse)
.map(SearchOption::getName);
obs.subscribe(name -> {
applySearchOptions.add(name);
}, e -> {
}, () -> {
showData(applySearchOptions);
});
Single<ArrayList<String>> obs = Observable.fromIterable(searchOptions)
.filter(SearchOption::isInUse)
.map(SearchOption::getName)
.collect(ArrayList<String>::new, List::add);
obs.subscribe(this::showData);

32. Q & A