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Java 8 Stream API Collectors for Guava Immutable Collections

With Java 8 Stream API you can collect the elements of your Stream using one of the many methods of the java.util.Collectors class.

To collect the elements in a java.util.List you would do this:

list.stream().collect(Collectors.toList());

But the List returned is a standard mutable JDK List. Those used to Guava that want to return an immutable collection like ImmutableList would have to do this:

list.stream().collect(Collectors.collectingAndThen(Collectors.toList(), ImmutableList::copyOf));

The guava-stream project provides java.util.stream.Collector implementations for Guava Immutable Collections, simplifying the code to just this:

list.stream().collect(MoreCollectors.toImmutableList());

guava-stream is available on Maven Central, and requires at least Java 8.

You can add this dependency to your Maven project:

<dependency>
  <groupId>me.yanaga</groupId>
  <artifactId>guava-stream</artifactId>
  <version>1.0</version>
</dependency>

Or if you are using Gradle:

compile "me.yanaga:guava-stream:1.0"

Currently we have Collector implementations for ImmutableList, ImmutableSet, ImmutableSortedSet, ImmutableMap, ImmutableSortedMap, ImmutableBiMap, ImmutableMultiset, ImmutableSortedMultiset, ImmutableMultimap, ImmutableListMultimap, ImmutableSetMultimap, and ImmutableTable.