如何将迭代器转换为流? [英] How to convert an Iterator to a Stream?

问题描述

我正在寻找一种简洁的方法来转换 Iterator 到 Stream 或更具体地说，将迭代器查看"为流.

I am looking for a concise way to convert an Iterator to a Stream or more specifically to "view" the iterator as a stream.

出于性能原因，我想避免在新列表中复制迭代器:

For performance reason, I would like to avoid a copy of the iterator in a new list:

Iterator<String> sourceIterator = Arrays.asList("A", "B", "C").iterator();
Collection<String> copyList = new ArrayList<String>();
sourceIterator.forEachRemaining(copyList::add);
Stream<String> targetStream = copyList.stream();

<小时>

根据评论中的一些建议，我也尝试使用 Stream.generate:

public static void main(String[] args) throws Exception {
    Iterator<String> sourceIterator = Arrays.asList("A", "B", "C").iterator();
    Stream<String> targetStream = Stream.generate(sourceIterator::next);
    targetStream.forEach(System.out::println);
}

但是，我得到一个 NoSuchElementException(因为没有调用 hasNext)

However, I get a NoSuchElementException (since there is no invocation of hasNext)

Exception in thread "main" java.util.NoSuchElementException
    at java.util.AbstractList$Itr.next(AbstractList.java:364)
    at Main$$Lambda$1/1175962212.get(Unknown Source)
    at java.util.stream.StreamSpliterators$InfiniteSupplyingSpliterator$OfRef.tryAdvance(StreamSpliterators.java:1351)
    at java.util.Spliterator.forEachRemaining(Spliterator.java:326)
    at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:580)
    at Main.main(Main.java:20)

我看过StreamSupport 和 集合 但我什么也没找到.

I have looked at StreamSupport and Collections but I didn't find anything.

推荐答案

一种方法是从 Iterator 创建一个 Spliterator 并将其用作流的基础:

One way is to create a Spliterator from the Iterator and use that as a basis for your stream:

Iterator<String> sourceIterator = Arrays.asList("A", "B", "C").iterator();
Stream<String> targetStream = StreamSupport.stream(
          Spliterators.spliteratorUnknownSize(sourceIterator, Spliterator.ORDERED),
          false);

另一种可能更具可读性的替代方法是使用 Iterable - 使用 lambda 从 Iterator 创建一个 Iterable 非常容易，因为Iterable 是一个函数式接口:

An alternative which is maybe more readable is to use an Iterable - and creating an Iterable from an Iterator is very easy with lambdas because Iterable is a functional interface:

Iterator<String> sourceIterator = Arrays.asList("A", "B", "C").iterator();

Iterable<String> iterable = () -> sourceIterator;
Stream<String> targetStream = StreamSupport.stream(iterable.spliterator(), false);

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