Java CompletableFuture thenCompose 与几个异步任务

Question

我有一个由 2 个异步步骤组成的过程。第二步基于第一步的结果运行。该过程在循环中启动。挑战在于第二步是由多个异步任务完成的，这些任务采用第一步迭代的输出。第一步完成后，我想使用第一步结果启动 n 秒步骤。我使用 CompletableFuture 和 thenCompose 编写了这段代码。

它有效，但我发现它非常复杂，我想知道这是否是正确的方法。我特别想知道第二级子任务的管理和使用 CompletableFuture.allOf 使其像一个单一的 CompletableFuture 是否是正确的做法.

public void test() {
    // Gather CompletableFutures to wait for them at the end
    List<CompletableFuture> futures = new ArrayList<>();

    // First steps
    for (int i = 0; i < 10; i++) {
        int finalI = i;
        CompletableFuture<Void> fut = CompletableFuture.supplyAsync(() -> {
            logger.debug("Start step 1 - " + finalI);
            simulateLongProcessing();// just waits for 1 s
            logger.debug("End step 1 - " + finalI);
            return "step1 output - " + finalI;
        }).thenCompose(s -> {
            List<CompletableFuture> subFutures = new ArrayList<>();
            // Second step : Launch several sub-tasks based on the result of the first step
            for (int j = 0; j < 50; j++) {
                final int finalJ = j;
                CompletableFuture<String> f = CompletableFuture.supplyAsync(() -> {
                    logger.debug("Start - step 2 : " + s + " | " + finalJ);
                    simulateLongProcessing();
                    logger.debug("End - step 2 : " + s + " | " + finalJ);
                    return "step2 output - " + s + " | " + finalJ;
                });
                subFutures.add(f);
            }
            return CompletableFuture.allOf(subFutures.toArray(new CompletableFuture[0]));
        });
        futures.add(fut);
    }

    // Wait for the completion
    for (CompletableFuture future : futures) {
        future.join();
    }
}

Answer 1

不要执行 CompletableFuture.supplyAsync在传递给 thenCompose 的函数中当您可以使用直接的 thenApplyAsync 链接相同的依赖函数时.

通过 thenApplyAsync 链接依赖函数允许您获得 CompletableFuture在第一步完成之前代表这些步骤的实例，因此您可以将它们全部收集到您的 List 中等待它们最后完成，不需要通过 CompletableFuture.allOf 创建复合 future .

public void test() {
    // Gather CompletableFutures to wait for them at the end
    List<CompletableFuture<?>> futures = new ArrayList<>();

    for (int i = 0; i < 10; i++) {
        int finalI = i;
        CompletableFuture<String> step1 = CompletableFuture.supplyAsync(() -> {
            logger.debug("Start step 1 - " + finalI);
            simulateLongProcessing();// just waits for 1 s
            logger.debug("End step 1 - " + finalI);
            return "step1 output - " + finalI;
        });
        // Second step : Chain several sub-tasks based on the result of the first step
        for (int j = 0; j < 50; j++) {
            final int finalJ = j;
            futures.add(step1.thenApplyAsync(s -> {
                logger.debug("Start - step 2 : " + s + " | " + finalJ);
                simulateLongProcessing();
                logger.debug("End - step 2 : " + s + " | " + finalJ);
                return "step2 output - " + s + " | " + finalJ;
            }));
        }
    }

    // Wait for the completion
    for (CompletableFuture<?> future : futures) {
        future.join();
    }
}