如何等待异步 Observable 完成 [英] How to wait for async Observable to complete

问题描述

我正在尝试使用 rxjava 构建示例.该示例应编排 ReactiveWareService 和 ReactiveReviewService，重新调整 WareAndReview 组合.

I'm trying to build a sample using rxjava. The sample should orchestrate a ReactiveWareService and a ReactiveReviewService retruning a WareAndReview composite.

ReactiveWareService
        public Observable<Ware> findWares() {
        return Observable.from(wareService.findWares());
    }

ReactiveReviewService: reviewService.findReviewsByItem does a ThreadSleep to simulate a latency!

public Observable<Review> findReviewsByItem(final String item) {
return Observable.create((Observable.OnSubscribe<Review>) observer -> executor.execute(() -> {
    try {
        List<Review> reviews = reviewService.findReviewsByItem(item);
        reviews.forEach(observer::onNext);
        observer.onCompleted();
    } catch (Exception e) {
        observer.onError(e);
    }
}));
}

public List<WareAndReview> findWaresWithReviews() throws RuntimeException {
final List<WareAndReview> wareAndReviews = new ArrayList<>();

wareService.findWares()
    .map(WareAndReview::new)
.subscribe(wr -> {
        wareAndReviews.add(wr);
        //Async!!!!
        reviewService.findReviewsByItem(wr.getWare().getItem())
            .subscribe(wr::addReview,
                throwable -> System.out.println("Error while trying to find reviews for " + wr)
            );
    }
);

//TODO: There should be a better way to wait for async reviewService.findReviewsByItem completion!
try {
    Thread.sleep(3000);
} catch (InterruptedException e) {}

return wareAndReviews;
}

鉴于我不想返回 Observable，我该如何等待异步 Observable (findReviewsByItem) 完成?

Given the fact I don't want to return an Observable, how can I wait for async Observable (findReviewsByItem) to complete?

推荐答案

你的大部分例子都可以用标准的 RxJava 操作符重写:

Most of your example can be rewritten with standard RxJava operators that work together well:

public class Example {

    Scheduler scheduler = Schedulers.from(executor);

    public Observable<Review> findReviewsByItem(final String item) {
        return Observable.just(item)
               .subscribeOn(scheduler)
               .flatMapIterable(reviewService::findReviewsByItem);
    }
    public List<WareAndReview> findWaresWithReviews() {
        return wareService
               .findWares()
               .map(WareAndReview::new)
               .flatMap(wr -> {
                   return reviewService
                          .findReviewsByItem(wr.getWare().getItem())
                          .doOnNext(wr::addReview)
                          .lastOrDefault(null)
                          .map(v -> wr);
               })
               .toList()
               .toBlocking()
               .first();
    }
}

每当您想组合这样的服务时，首先要考虑 flatMap.你不需要为每个子 Observable 阻塞，但如果真的有必要，只需要在最后使用 toBlocking().

Whenever you want to compose services like this, think of flatMap first. You don't need to block for each sub-Observable but only at the very end with toBlocking() if really necessary.

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