// this is just the standard way of turning an iterator of unknown size into a stream.
  public static <T> Stream<T> toStream(Iterator<T> iterator) {
    return StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false);
  }

  public static void main(String[] args) {
    final Stream<Integer> ints1 = Stream.of(1,2,3)
        .peek(value -> System.out.println("peek1.value = " + value));

    final Stream<Integer> ints2 = Stream.of(1).flatMap(s -> ints1)
        .peek(value -> System.out.println("peek2.value = " + value));

    final List<Integer> collect = toStream(ints2.iterator())
        .peek(value -> System.out.println("peek3.value = " + value))
        .collect(Collectors.toList());

    System.out.println("collect.size() = " + collect.size());
  }