Convert an Iterable to Stream in Java

This post will discuss how to convert an iterable to stream in Java.

1. Using `Spliterators`

The Iterable interface did not provide stream() or parallelStream() methods, mainly due to design issues to avoid unpredictable results. The technical discussion can be found in this thread. Instead, they added spliterator() default method to the Iterable interface.

So, the idea is to get Spliterator over the elements described by the Iterable by calling its spliterator() method and then pass the Spliterator to StreamSupport.stream() to get a new sequential or parallel stream.

import java.util.Arrays;

import java.util.stream.Collectors;

import java.util.stream.Stream;

import java.util.stream.StreamSupport;

class Main

{

// Generic method to convert an Iterable to a Stream

public static <T> Stream<T> iterableToStream(Iterable<T> iterable)

{

// get spliterator from Iterable and turn it into a sequential stream

return StreamSupport.stream(iterable.spliterator(), false);

}

public static void main(String[] args)

{

Iterable<String> iterable = Arrays.asList("A", "B", "C", "D");

Stream<String> stream = iterableToStream(iterable);

System.out.println(stream.collect(Collectors.toList()));

}

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Output:

[A, B, C, D]

2. Using Guava Library

Guava release 21.0 introduced several new classes such as Streams, Comparators, MoreCollectors, etc. The Streams class has many utility classes for working with java.util.stream.Stream. One such method is stream(), which can create a sequential stream of the contents of the iterable.

Please note that if the Iterable is not an instance of Collection, this method internally calls StreamSupport.stream() to get a sequential stream from Spliterator; otherwise, it simply calls Collection.stream() method.

import com.google.common.collect.Streams;

import java.util.Arrays;

import java.util.stream.Collectors;

import java.util.stream.Stream;

class Main

{

// Generic method to convert an Iterable to a Stream

public static <T> Stream<T> iterableToStream(Iterable<T> iterable)

{

// Returns a sequential stream of the contents of the iterable

return Streams.stream(iterable);

}

public static void main(String[] args)

{

Iterable<String> iterable = Arrays.asList("A", "B", "C", "D");

Stream<String> stream = iterableToStream(iterable);

System.out.println(stream.collect(Collectors.toList()));

}

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Output:

[A, B, C, D]

That’s all about converting an Iterable to Stream in Java.

Also See:

Create a sequential Stream from an iterator in Java

Convert an Iterable to Stream in Java

1. Using Spliterators

2. Using Guava Library

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1. Using `Spliterators`