Convert Iterable to Stream using Java 8 JDK

Question

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?

Answer 1

There's a much better answer than using spliteratorUnknownSize directly, which is both easier and gets a better result. Iterable has a spliterator() method, so you should just use that to get your spliterator. 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:

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

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

Answer 2

If you can use Guava library, since version 21, you can use

Streams.stream(iterable)