Question

我有一个完整的将来代码，该代码将引发NPE。我无法在本地复制该异常。

我已经为代码尝试了验收测试和单元测试，但是没有给出确切的错误响应。

    final List<CompletableFuture<Map<K, V>>> completableFutures = 
    copy.stream()                                                                         
    .map(copy -> getRespForId(requestContext, copy))                                                                          
    .collect(Collectors.toList());

    return CompletableFuture.allOf(completableFutures.toArray(new CompletableFuture<?>[0]))
               .thenApply(future -> completableFutures.stream()
                                        .map(CompletableFuture::join)
                                        .flatMap(longMap -> longMap.entrySet().stream())
                                        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)));

预期是

Caused by: java.util.concurrent.CompletionException: java.lang.NullPointerException
    at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source)
    at java.base/java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source)
    at java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(Unknown Source)
    at java.base/java.util.concurrent.CompletableFuture.postComplete(Unknown Source)
    at java.base/java.util.concurrent.CompletableFuture.postFire(Unknown Source)
    at java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(Unknown Source)
    at java.base/java.util.concurrent.CompletableFuture$Completion.exec(Unknown Source)
    at java.base/java.util.concurrent.ForkJoinTask.doExec(Unknown Source)
    at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(Unknown Source)
    at java.base/java.util.concurrent.ForkJoinPool.scan(Unknown Source)
    at java.base/java.util.concurrent.ForkJoinPool.runWorker(Unknown Source)
    at java.base/java.util.concurrent.ForkJoinWorkerThread.run(Unknown Source)
Caused by: java.lang.NullPointerException: null
    at java.base/java.util.Objects.requireNonNull(Unknown Source)
    at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Unknown Source)

Answer 1

这里的问题不是键而是值。您会收到此异常，因为值为 null。看起来 java.util.stream.Collectors#uniqKeysMapAccumulator 检查 Objects.requireNonNull 的值。见NullPointerException in Collectors.toMap with null entry values

如何在可完成的将来识别空指针异常？

1 个答案: