Java Stream API -- How to reduce a loop to reduce

Question

I have the following statement:

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();
};

Is it possible to convert a loop in the inner lambda to a smart stream.reduce operation (or other aggregation)? I'd tried various approaches but I failed.

Greetings, JG.

Jorn Vernee · Accepted Answer · 2017-01-03 13:23:18Z

5

You could use flatMap instead:

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.

answered Jan 3, 2017 at 13:23

Jorn Vernee

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