如何使用 Reactor 3.x 将 List<T> 转换为 Flux<T>

Question

我有一个异步调用 thrift 接口：

public CompletableFuture<List<Long>> getFavourites(Long userId){
    CompletableFuture<List<Long>> future = new CompletableFuture();
    OctoThriftCallback callback = new OctoThriftCallback(thriftExecutor);
    callback.addObserver(new OctoObserver() {
        @Override
        public void onSuccess(Object o) {
            future.complete((List<Long>) o);
        }

        @Override
        public void onFailure(Throwable throwable) {
            future.completeExceptionally(throwable);
        }
    });
    try {
        recommendAsyncService.getFavorites(userId, callback);
    } catch (TException e) {
        log.error("OctoCall RecommendAsyncService.getFavorites", e);
    }
    return future;
}

现在它 returns 一个 CompletableFuture。然后我调用它来使用 Flux 做一些处理器。

public Flux<Product> getRecommend(Long userId) throws InterruptedException, ExecutionException, TimeoutException {
    // do not like it
    List<Long> recommendList = wrapper.getRecommend(userId).get(2, TimeUnit.SECONDS);

    System.out.println(recommendList);
    return Flux.fromIterable(recommendList)
            .flatMap(id -> Mono.defer(() -> Mono.just(Product.builder()
                    .userId(userId)
                    .productId(id)
                    .productType((int) (Math.random()*100))
                    .build())))
            .take(5)
            .publishOn(mdpScheduler);
}

但是，我想从 getFavourites 方法中获取一个 Flux，我可以在 getRecommend 方法中使用它。
或者，你可以推荐一个 Flux API ，我可以将 List<Long> recommendList 转换为 Flux<Long> recommendFlux.

Answer 1

要将 CompletableFuture<List<T>> 转换为 Flux<T>，您可以使用 Mono#fromFuture with Mono#flatMapMany:

var future = new CompletableFuture<List<Long>>();
future.completeAsync(() -> List.of(1L, 2L, 3L, 4L, 5L),
    CompletableFuture.delayedExecutor(3, TimeUnit.SECONDS));

Flux<Long> flux = Mono.fromFuture(future).flatMapMany(Flux::fromIterable);

flux.subscribe(System.out::println);

在回调中异步接收的

List<T> 也可以在不使用 CompletableFuture 的情况下转换为 Flux<T>。可以直接使用Mono#create with Mono#flatMapMany:

Flux<Long> flux = Mono.<List<Long>>create(sink -> {
  Callback<List<Long>> callback = new Callback<List<Long>>() {
    @Override
    public void onResult(List<Long> list) {
      sink.success(list);
    }

    @Override
    public void onError(Exception e) {
      sink.error(e);
    }
  };
  client.call("query", callback);
}).flatMapMany(Flux::fromIterable);

flux.subscribe(System.out::println);

或者简单地使用 Flux#create 一次通过多次发射：

Flux<Long> flux = Flux.create(sink -> {
  Callback<List<Long>> callback = new Callback<List<Long>>() {
    @Override
    public void onResult(List<Long> list) {
      list.forEach(sink::next);
    }

    @Override
    public void onError(Exception e) {
      sink.error(e);
    }
  };
  client.call("query", callback);
});

flux.subscribe(System.out::println);

如何使用 Reactor 3.x 将 List<T> 转换为 Flux<T>

How to convert List<T> to Flux<T> by using Reactor 3.x

java

reactive-programming

project-reactor