[java] 반복자를 스트림으로 변환하는 방법?

나는 변환하는 간결한 방법을 찾고 있는데요 IteratorA를 Stream“보기”스트림으로 반복자 또는 더 구체적으로.

성능상의 이유로 새 목록에서 반복자의 사본을 피하고 싶습니다.

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

의견의 몇 가지 제안을 바탕으로 다음과 같이 사용하려고했습니다 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);
}

그러나 NoSuchElementException(의 호출이 없기 때문에 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)

나는 살펴 보았다 StreamSupport및 Collections하지만 난 아무것도 찾지 못했습니다.

답변

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

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

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

public class StreamUtils {

    public static <T> Stream<T> asStream(Iterator<T> sourceIterator) {
        return asStream(sourceIterator, false);
    }

    public static <T> Stream<T> asStream(Iterator<T> sourceIterator, boolean parallel) {
        Iterable<T> iterable = () -> sourceIterator;
        return StreamSupport.stream(iterable.spliterator(), parallel);
    }
}

List<String> aPrefixedStrings = asStream(sourceIterator)
                .filter(t -> t.startsWith("A"))
                .collect(toList());

Stream.generate(() -> null)
    .takeWhile(x -> iterator.hasNext())
    .map(n -> iterator.next())
    .forEach(System.out::println);

Spliterator<Model> spliterator = Spliterators.spliteratorUnknownSize(
        iterator, Spliterator.NONNULL);
Stream<Model> stream = StreamSupport.stream(spliterator, false);

import com.google.common.collect.Streams;

Streams.stream(iterator)
       .map(v-> function(v))
       .collect(Collectors.toList());