[SOLVED] Convert Iterable to Stream using Java 8 JDK

Convert Iterable to Stream using Java 8 JDK

I have an interface which returns java.lang.Iterable<T>.

I would like to manipulate that result using the Java 8 Stream API.

However Iterable can't "stream".

Any idea how to use the Iterable as a Stream without converting it to List?

Solution

Iterable has a spliterator() method, which you can pass to StreamSupport.stream to create a stream:

StreamSupport.stream(iterable.spliterator(), false)
             .filter(...)
             .moreStreamOps(...);

This is a much better answer than using spliteratorUnknownSize directly, as it is both easier and gets a better result. In the worst case, it's the same code (the default implementation uses spliteratorUnknownSize), but in the more common case, where your Iterable is already a collection, you'll get a better spliterator, and therefore better stream performance (maybe even good parallelism). It's also less code.

As you can see, getting a stream from an Iterable (see also this question) is not very painful.