在filter（）操作过滤掉所有内容后，Java流findAny（）遇到空指针异常 [英] Java streams findAny() encounters null pointer exception after filter() operation filters out everything

问题描述

我无法确定为什么 findAny（）在 filter（）操作之后抛出空指针异常流。在这个特定的测试用例中，过滤器操作应该已经过滤掉了所有内容，没有留下 findAny（）的结果。

I am having trouble figuring why findAny() throws a null pointer exception after filter() operation on a stream. In this particular test case, the filter operation should have filtered out everything, leaving no results for findAny().

Optional<JsonNode> encryption = sseEncryptionList.stream()
                  .filter(n -> n.textValue().equals("AES256")) //Filters out everything
                  .findAny(); //Throws null pointer exception

堆栈跟踪：

Exception in thread "main" java.lang.NullPointerException
at example.Main.lambda$main$0(Main.java:41)
at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174)
at java.util.ArrayList$ArrayListSpliterator.tryAdvance(ArrayList.java:1351)
at java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:126)
at java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:498)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:485)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
at java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.findAny(ReferencePipeline.java:469)
at example.Main.main(Main.java:42)

findAny（）的预期行为是否抛出空指针如果流不包含任何元素，则会出现异常吗？

Is this expected behavior for findAny() to throw a null pointer exception if the stream doesn't contain any elements?

编辑：解析可能过滤掉所有元素的过滤操作的优雅且实用的方法是什么？

What is an elegant and functional way to resolve filter operations that might filter out all elements?

推荐答案

避免NPE的最佳方法是：

The best way to avoid NPE is:

Optional<JsonNode> encryption = sseEncryptionList.stream()
              .filter(Objects::nonNull)
              .filter(n -> "AES256".equals(n.textValue()))
              .findAny();

AES256.equals（n.textValue（）））将不会抛出NPE

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