CompletableFuture allOf example 예제

IO가 오래걸리는 작업(db 또는 타 서비스 호출)에 CompletableFuture를 이용하면 쉽게 병렬 처리를 할 수 있습니다.

물론 db의 connection pool, 타 서비스 호출 시에 해당 서비스에서 감당할 수 있는 정도를 확인하고 상황에 맞게 동시 실행 Thread 개수를 지정합니다.

 

List<CompletableFuture<String>> completableFutures = new ArrayList<>();

		ExecutorService executorService = Executors.newFixedThreadPool(100);

		IntStream.rangeClosed(1, 100)
				.forEach(i -> {
					CompletableFuture<String> completableFuture =
							CompletableFuture.supplyAsync(() -> {
								String threadName = Thread.currentThread().getName();
								System.out.println("task start - " + threadName);
								try {
									Thread.sleep(2000);
								} catch (InterruptedException e) {
									throw new RuntimeException(e);
								}

								return i + " - " + threadName;
							}, executorService);

					completableFutures.add(completableFuture);
				});

		CompletableFuture<String>[] cfs =
				(CompletableFuture<String>[]) completableFutures.toArray(new CompletableFuture[completableFutures.size()]);

		CompletableFuture.allOf(cfs)
				.thenApply(v -> completableFutures.stream()
						.map(CompletableFuture::join)
						.collect(toList())
				);

		List<String> collect = Arrays.stream(cfs)
				.map(CompletableFuture::join)
				.collect(toList());

		System.out.println(collect.size());

 

CompletableFuture를 잘 사용해서 동시성 프로그램을 작성해보세요

 

참고

https://www.baeldung.com/java-completablefuture

Guide To CompletableFuture | Baeldung

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html

CompletableFuture (Java Platform SE 8 )

https://codechacha.com/ko/java-completable-future/

Java - CompletableFuture 사용 방법