An ImmutableMultimapCollector in Java

ImmutableMultimapCollector.java

import com.google.common.collect.ImmutableMultimap;
import com.google.common.collect.ImmutableSet;

import java.util.Map;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

public class ImmutableMultimapCollector<K, V> implements Collector<Map.Entry<K, V>, ImmutableMultimap.Builder<K, V>, ImmutableMultimap<K, V>> {
    @Override
    public Supplier<ImmutableMultimap.Builder<K, V>> supplier() {
        return ImmutableMultimap::builder;
    }

    @Override
    public BiConsumer<ImmutableMultimap.Builder<K, V>, Map.Entry<K, V>> accumulator() {
        return (kvBuilder, kvEntry) -> kvBuilder.put(kvEntry.getKey(), kvEntry.getValue());
    }

    @Override
    public BinaryOperator<ImmutableMultimap.Builder<K, V>> combiner() {
        return (kvBuilder, kvBuilder2) -> ImmutableMultimap.<K, V>builder()
                .putAll(kvBuilder.build())
                .putAll(kvBuilder2.build());
    }

    @Override
    public Function<ImmutableMultimap.Builder<K, V>, ImmutableMultimap<K, V>> finisher() {
        return ImmutableMultimap.Builder::build;
    }

    @Override
    public Set<Characteristics> characteristics() {
        return ImmutableSet.of(Characteristics.CONCURRENT, Characteristics.UNORDERED);
    }
}

Usage.java

private Map<String, Collection<String>> exampleUsage(URI targetPath) {
    return URLEncodedUtils.parse(targetPath, "UTF-8").stream()
            .map(pair -> new AbstractMap.SimpleImmutableEntry<>(pair.getName(), pair.getValue()))
            .collect(new ImmutableMultimapCollector<>())
            .asMap();
}