问题描述
我正在Java 8中使用Completable future,并且我想编写一种方法,该方法基于接收到的参数并行运行具有副作用的多个任务,然后返回其合并的" future(使用CompletableFuture.allOf()
),或什么也不做,并返回一个已经完成的未来.
I am using Completable futures in java 8 and I want to write a method that, based on a received parameter, either runs multiple tasks with side effects in parallel and then return their "combined" future (using CompletableFuture.allOf()
), or does nothing and returns an already-completed future.
但是,allOf
返回一个CompletableFuture<Void>
:
public static CompletableFuture<Void> allOf(CompletableFuture<?>... cfs)
创建已知的已经完成的未来的唯一方法是使用completedFuture()
,它需要一个值:
And the only way to create an already-completed future that know is using completedFuture()
, which expects a value:
public static <U> CompletableFuture<U> completedFuture(U value)
和Void
是不可实例化的,所以我需要另一种方法来创建类型为CompletableFuture<Void>
的已经完成的future.
and Void
is uninstantiable, so I need another way to create an already-completed future of type CompletableFuture<Void>
.
做到这一点的最佳方法是什么?
What is the best way to do this?
推荐答案
由于无法实例化Void
,因此只能用null
结果完成CompletableFuture<Void>
,而这恰恰是在得到null
结果时得到的结果.成功完成后,在allOf()
返回的将来调用join()
.
Since Void
can not be instantiated, you can only complete a CompletableFuture<Void>
with a null
result, which is exactly what you also will get when calling join()
on the future returned by allOf()
once it has been successfully completed.
因此您可以使用
CompletableFuture<Void> cf = CompletableFuture.completedFuture(null);
获得这样一个已经完成的未来.
to get such an already completed future.
但是您也可以使用
CompletableFuture<Void> cf = CompletableFuture.allOf();
表示不存在结果依赖的作业.结果将完全相同.
to denote that there are no jobs the result depends on. The result will be exactly the same.
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