Convert Iterable to Stream using Java 8 JDK

Question

I have an interface which returns java lang Iterable lt T gt    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

User · Answer

You can easily create a Stream out of an Iterable or Iterator   public static  lt T gt  Stream lt T gt  stream Iterable lt T gt  iterable        return StreamSupport stream          Spliterators spliteratorUnknownSize              iterable iterator                Spliterator ORDERED                    false

User · Answer

Another way to do it  with Java 8 and without external libs   Stream concat collectionA stream    collectionB stream           collect Collectors toList

User · Answer

If you happen to use Vavr formerly known as Javaslang   this can be as easy as   Iterable i         Stream ofAll i

User · Answer

If you can use Guava library  since version 21  you can use  Streams stream iterable

User · Answer

A very simple work-around for this issue is to create a Streamable lt T gt  interface extending Iterable lt T gt  that holds a default  lt T gt  stream   method   interface Streamable lt T gt  extends Iterable lt T gt        default Stream lt T gt  stream             return StreamSupport stream spliterator    false             Now any of your Iterable lt T gt s can be trivially made streamable just by declaring them implements Streamable lt T gt  instead of Iterable lt T gt

User · Answer

I ve created this class   public class Streams                  Converts Iterable to stream             public static  lt T gt  Stream lt T gt   streamOf final Iterable lt T gt  iterable            return toStream iterable  false                         Converts Iterable to parallel stream             public static  lt T gt  Stream lt T gt  parallelStreamOf final Iterable lt T gt  iterable            return toStream iterable  true              private static  lt T gt  Stream lt T gt  toStream final Iterable lt T gt  iterable  final boolean isParallel            return StreamSupport stream iterable spliterator    isParallel             I think it s perfectly readable because you don t have to think about spliterators and booleans  isParallel

User · Answer

So as another answer mentioned Guava has support for this by using   Streams stream iterable     I want to highlight that the implementation does something slightly different than other answers suggested  If the Iterable is of type Collection they cast it   public static  lt T gt  Stream lt T gt  stream Iterable lt T gt  iterable      return  iterable instanceof Collection          Collection lt T gt   iterable  stream         StreamSupport stream iterable spliterator    false      public static  lt T gt  Stream lt T gt  stream Iterator lt T gt  iterator      return StreamSupport stream      Spliterators spliteratorUnknownSize iterator  0       false

User · Answer

I would like to suggest using JOOL library  it hides spliterator magic behind the Seq seq iterable  call and also provides a whole bunch of additional useful functionality

User · Answer

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

[java] Convert Iterable to Stream using Java 8 JDK

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