Custom thread pool in Java 8 parallel stream

Question

Is it possible to specify a custom thread pool for Java 8 parallel stream? I can not find it anywhere.

Imagine that I have a server application and I would like to

Answer 1

To measure the actual number of used threads, you can check Thread.activeCount():

    Runnable r = () -> IntStream
            .range(-42, +42)
            .parallel()
            .map(i -> Thread.activeCount())
            .max()
            .ifPresent(System.out::println);

    ForkJoinPool.commonPool().submit(r).join();
    new ForkJoinPool(42).submit(r).join();

This can produce on a 4-core CPU an output like:

5 // common pool
23 // custom pool

Without .parallel() it gives:

3 // common pool
4 // custom pool