org.decampo.examples.collections.MoreCollectors.java Source code

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Here is the source code for org.decampo.examples.collections.MoreCollectors.java

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/*
 * This is free and unencumbered software released into the public domain.
 * 
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 * 
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 * 
 * For more information, please refer to <http://unlicense.org/>
 */
package org.decampo.examples.collections;

import java.util.function.Function;
import java.util.stream.Collector;
import org.apache.commons.collections4.SetValuedMap;
import org.apache.commons.collections4.multimap.HashSetValuedHashMap;

/**
 *
 * @author ray@decampo.org
 */
public class MoreCollectors {
    public static <T, K, V> Collector<T, SetValuedMap<K, V>, SetValuedMap<K, V>> toSetValuedMap(
            Function<T, K> keyMapper, Function<T, V> valueMapper) {

        return Collector.of(HashSetValuedHashMap::new,
                (map, t) -> map.put(keyMapper.apply(t), valueMapper.apply(t)), (map1, map2) -> {
                    map1.putAll(map2);
                    return map1;
                }, Collector.Characteristics.IDENTITY_FINISH, Collector.Characteristics.UNORDERED);
    }

    public static <T, K> Collector<T, SetValuedMap<K, T>, SetValuedMap<K, T>> groupingByDistinct(
            Function<T, K> classifier) {

        return toSetValuedMap(classifier, Function.identity());
    }
}