加入后在 CompletableFuture 中返回一个列表

Question

我有这段代码：

List<PendingWorkflowReturn> pendingWorkflowReturns = new ArrayList<>();

        CompletableFuture<List<PendingWorkflowReturn>> cf1 
                = CompletableFuture.supplyAsync(()-> 
                pendingWorkflows(menageReturn.getId(),"a"));

        CompletableFuture<List<PendingWorkflowReturn>> cf2
                = CompletableFuture.supplyAsync(()->
                pendingWorkflows(menageReturn.getId(),"b"));


        List<PendingWorkflowReturn> combined = Stream.of(cf1,cf2)
                .map(CompletableFuture::join).collect(Collectors.toList());

我想return一个List，但是return在一个list中的一个list

Answer 1

如果你想按顺序连接两个列表，你可以flatMap将它们放入流中：

    List<PendingWorkflowReturn> combined = Stream.of(cf1,cf2)
            .map(CompletableFuture::join)
            .flatMap(List::stream) // this replaces each list with the elements of the list in the stream
            .collect(Collectors.toList());

或者，您可以使用自定义收集器：

    List<PendingWorkflowReturn> combined = Stream.of(cf1,cf2)
            .map(CompletableFuture::join)
            .collect(ArrayList::new, ArrayList::addAll, ArrayList::addAll);