CompletableFuture如何先返回FALSE或等到全部完成后再返回TRUE [英] CompletableFuture how to return first FALSE or wait until all are completed to return TRUE

问题描述

我有些奇怪的情况，似乎不允许这种钉子钉入任何已广泛建立的CompletableFuture孔中.

I have a bit of an odd situation that doesn’t seem to allow this peg to fit into any of the widely established CompletableFuture holes.

• 在一个用于评估返回的布尔值的主要方法中，我想允许对三种不同方法的调用以异步方式完成.这三种方法都可以返回TRUE或FALSE.
• 如果 any 返回FALSE，我希望评估结果除去其余部分，然后简单地返回该FALSE值.关键是，它可以是三个中的任何，不一定是第一个.
• 但最重要的是，我需要评估，直到所有三个 返回TRUE为止，然后才真正返回TRUE.这是非常重要的.

• Within a primary method that is evaluating returned booleans, I am wanting to allow calls to three different methods to complete asynchronously. Each of these three methods can return either a TRUE or a FALSE.
• If any return a FALSE, I want the evaluation to drop the remainder and simply return that FALSE value. The point being, it can be any of the three, not necessarily the first.
• But most importantly, I need the evaluation to wait until all three return TRUE before actually returning TRUE. This is critically important.

现在，我正在使用基本的&& 链进行此评估:

Right now, I am using a basic && chain to make this evaluation:

public boolean evaluateChecks() {
    return checkOne().Join() && checkTwo().Join() && checkThree().Join();
}

但是，这仍然按照特定的顺序执行操作-如果 checkThree()是第一个返回FALSE值的对象，它仍然必须等到前两个提供了它们的值之后才能进行评估，因为&& 掉线的工作原理.

However this still does things in a specific order - if checkThree() is the first to return a FALSE value, it still has to wait until the prior two have provided their values before it gets evaluated, due to how the && fall-through works.

现在，所有这三种方法都返回 CompletableFuture< Boolean> ，但我可以将它们还原回普通方法以在主要方法中运行 CompletableFuture 的方法没有问题.对它们进行评估.

Right now all three methods return CompletableFuture<Boolean>, but I have no problem reverting these back into normal methods in order to run a CompletableFuture in the primary method that evaluates them.

我查看了很多示例，但似乎没有一个可以为我提供所需的功能.

I have looked at quite a few examples, but none seem to provide me with the functionality I need.

推荐答案

从Didier L的答案改编而成:

Adapted from the answer by Didier L here:

• 如何实现CompletableFuture.allOf()一旦任何期货失败，交易会异常完成吗?

使用 thenAccept 来完成 CompletableFuture ，而不是使用 exceptionally 和 completeExceptionally >由 allOf()返回.

Instead of using exceptionally and completeExceptionally, use thenAccept to complete the CompletableFuture returned by allOf().

例如，保存期货，因为您要对它们进行连锁操作:

For example, save the futures because you're about to chain actions on them:

CompletableFuture<Boolean> a = checkOne(), b = checkTwo(), c = checkThree();

使用

Use CompletableFuture.allOf to wait for all of them to complete (presumably you're not expecting failures/exceptions) and transform the Void result into the expected Boolean value of true.

CompletableFuture<Boolean> allWithFailFast = CompletableFuture.allOf(a, b, c).thenApply(__ -> a.join() && b.join() && c.join());
// if there is an exception, it'll be propagated to the future returned by thenApply

有了上面返回的 CompletableFuture ，如果任何原始期货以 false 完成，您现在可以更快地完成 complete .

With the returned CompletableFuture above, you can now complete it faster if any of the original futures completes with false.

Stream.of(a, b, c).forEach(f -> f.thenAccept(result -> {
    if (!result) {
        allWithFailFast.complete(false);
    }
}));

根据完成顺序及其结果， allOf 期货将首先完成，并带有评估期货的结果，或者其中一个期货将返回 false ，并且导致 allWithFailFast 以 false 完成.

Depending on the order of completions and their result, either the allOf future will complete first with a result of evaluating the futures or one of the futures will return false and cause the allWithFailFast to complete with false.

如果多个期货都以 false 完成，则只有第一个调用

If multiple futures complete with false, only the first call to

allWithFailFast.complete(false);

会做任何事情，其他的基本上都会被忽略.

will do anything, the others will essentially be ignored.

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