Java Stream API——如何减少一个循环来减少

Question

我有以下声明:

Function<Stream<Supplier<Collection<? extends User>>>, Stream<User>> userStreamSupplier =
   supStream -> {
    ArrayList<User> list = new ArrayList<>();
    supStream.forEach(sup -> list.addAll(sup.get()));
    return list.stream();
};

是否可以将内部 lambda 中的循环转换为智能stream.reduce 操作(或其他聚合)？我尝试过各种方法，但都失败了。

您好，JG。

Answer 1

您可以使用flatMap相反:

supStream -> supStream.flatMap(supp -> supp.get().stream());

Returns a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.