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Utility classes.

There is a newer version: 8.4.5

package org.molgenis.util.stream;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;
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 {
  private 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;
        });
  }
}