Java CompletableFuture.allOf() 找不到任何数组元素

一个非常简单的代码片段如下:

String[] list = {"a", "b", "c"};
List<CompletableFuture<String>> completableFutureList = new ArrayList<>();
for (String s : list) {
    completableFutureList.add(CompletableFuture.supplyAsync(() -> s)
            .thenApply(String::toUpperCase));
}
CompletableFuture<String>[] a = completableFutureList
        .toArray(new CompletableFuture[completableFutureList.size()]);
System.out.println(a.length);
CompletableFuture.allOf(a).whenComplete((r, e) -> {
    if (null != r) {
        System.out.println(r);
    } else {
        throw new RuntimeException(e);
    }
});

我希望程序应该打印“A B C”。但实际上没有打印任何内容。为什么以及如何解决这个问题？

 

最佳答案

引用 CompletableFuture.allOf() 的 Javadoc方法(强调我的):

Returns a new CompletableFuture that is completed when all of the given CompletableFutures complete. If any of the given CompletableFutures complete exceptionally, then the returned CompletableFuture also does so, with a CompletionException holding this exception as its cause. Otherwise, the results, if any, of the given CompletableFutures are not reflected in the returned CompletableFuture, but may be obtained by inspecting them individually. If no CompletableFutures are provided, returns a CompletableFuture completed with the value {@code null}.

所以我认为您需要在 a[0].get() 中手动查询它们(例如使用 whenComplete())。打回来。像这样的东西:

CompletableFuture.allOf(a).whenComplete((r, e) -> {
    for (CompletableFuture<String> future : a) {
        try {
           System.out.println(future.get());
        }
        catch (InterruptedException | ExecutionException e1) {
           e1.printStackTrace();
        }
    }
});

 

关于Java CompletableFuture.allOf() 找不到任何数组元素，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54365047/

 https://www.coder.work/article/5675495