org.molgenis.util.stream.MultimapCollectors Maven / Gradle / Ivy

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package org.molgenis.util.stream;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.LinkedHashMultimap;
import com.google.common.collect.Multimap;

import java.util.Map.Entry;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;

/**
 * Collectors that collect to {@link Multimap}.
 * 
 * see {@link Collectors#toMap(Function, Function)}, the equivalent of which is not (yet?) present in guava for the
 * {@link Multimap}.
 */
public class MultimapCollectors
{
	public static  Collector, ArrayListMultimap> toArrayListMultimap(
			Function keyGenerator, Function valueGenerator)
	{
		return toMultimap(ArrayListMultimap::create, keyGenerator, valueGenerator);
	}

	public static , E> Collector toMultimap(Supplier supplier,
			Function keyGenerator, Function valueGenerator)
	{
		return Collector.of(supplier, (map, entry) -> map.put(keyGenerator.apply(entry), valueGenerator.apply(entry)),
				(map1, map2) ->
				{
					map1.putAll(map2);
					return map1;
				});
	}

	public static > Collector, A, A> toMultimap(Supplier supplier)
	{
		return toMultimap(supplier, Entry::getKey, Entry::getValue);
	}

	public static  Collector, LinkedHashMultimap, LinkedHashMultimap> toLinkedHashMultimap()
	{
		return toMultimap(LinkedHashMultimap::create);
	}
}