com.softicar.platform.common.container.map.SetMapCollector Maven / Gradle / Ivy

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The SoftiCAR Platform is a lightweight, Java-based library to create interactive business web applications.

There is a newer version: 50.0.0

package com.softicar.platform.common.container.map;

import java.util.EnumSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Map.Entry;
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;

/**
 * A {@link Collector} for {@link Map} with {@link Set}.
 * 
 * TODO create unit test
 *
 * @author Oliver Richers
 */
public class SetMapCollector implements Collector>, Map>> {

	private final Function keyExtractor;
	private final Function valueExtractor;
	private final Supplier>> mapFactory;
	private final Supplier> setFactory;

	private SetMapCollector(Function keyExtractor, Function valueExtractor, Supplier>> mapFactory,
			Supplier> setFactory) {

		this.keyExtractor = keyExtractor;
		this.valueExtractor = valueExtractor;
		this.mapFactory = mapFactory;
		this.setFactory = setFactory;
	}

	public static  SetMapCollector of(Function keyExtractor) {

		// TODO cannot use HashMap::new because of defect in javac
		return new SetMapCollector<>(keyExtractor, Function.identity(), () -> new HashMap<>(), HashSet::new);
	}

	public static  SetMapCollector of(Function keyExtractor, Supplier>> mapFactory,
			Supplier> setFactory) {

		return new SetMapCollector<>(keyExtractor, Function.identity(), mapFactory, setFactory);
	}

	public static  SetMapCollector of(Function keyExtractor, Function valueExtractor) {

		// TODO cannot use HashMap::new because of defect in javac
		return new SetMapCollector<>(keyExtractor, valueExtractor, () -> new HashMap<>(), HashSet::new);
	}

	public static  SetMapCollector of(Function keyExtractor, Function valueExtractor,
			Supplier>> mapFactory, Supplier> setFactory) {

		return new SetMapCollector<>(keyExtractor, valueExtractor, mapFactory, setFactory);
	}

	@Override
	public Supplier>> supplier() {

		return mapFactory;
	}

	@Override
	public BiConsumer>, T> accumulator() {

		return (map, element) -> accumulate(map, element);
	}

	@Override
	public BinaryOperator>> combiner() {

		return this::combine;
	}

	@Override
	public Function>, Map>> finisher() {

		return map -> map;
	}

	@Override
	public Set characteristics() {

		return EnumSet.of(Characteristics.IDENTITY_FINISH);
	}

	private void accumulate(Map> map, T element) {

		K key = keyExtractor.apply(element);
		V value = valueExtractor.apply(element);
		getOrCreateSet(map, key).add(value);
	}

	private Map> combine(Map> map1, Map> map2) {

		for (Entry> entry: map2.entrySet()) {
			getOrCreateSet(map1, entry.getKey()).addAll(entry.getValue());
		}
		return map1;
	}

	private Set getOrCreateSet(Map> map, K key) {

		Set set = map.get(key);
		if (set == null) {
			map.put(key, set = setFactory.get());
		}
		return set;
	}
}