Java Streams-如果存在比较器,则排序

你可以这样做:

Stream<Something> stream = [...].stream().map()[...]; // preliminary processing
if(comparator != null) {
    stream = stream.sorted(comparator); // optional sorting
}
stream... // resumed processing, which ends in some terminal operation (such as collect)

Optional :

Stream<Whatever> stream = [...].stream().map()[...];

List<WhateverElse> result = Optional.ofNullable(comparator)
    .map(stream::sorted)
    .orElse(stream)
    .[...] // <-- go on with the stream pipeline
    .collect(Collectors.toList());

 Comparator<E> NO_SORTING = (one, other) -> 0;

.sorted(comparator.orElse(NO_SORTING))

如果你不介意使用第三方图书馆 StreamEx

StreamEx(source).[...].chain(s -> comparator == null ? s : s.sorted(comparator)).[...];

您可以使用辅助功能来实现这一点。

static <T, R> R applyFunction(T obj, Function<T, R> f) {
    return f.apply(obj);
}

applyFunction([...].stream().map()[...],
    stream -> comparator == null ? stream : stream.sorted(comparator))
    [...];

您不需要知道中间流类型。