add method

CHANGELOG.md

@@ -11,6 +11,7 @@
 * 【core   】     合成注解SyntheticAnnotation提取为接口，并为实现类添加注解选择器和属性处理器（pr#678@Gitee）
 * 【core   】     增加BeanValueProvider（issue#I5FBHV@Gitee）
 * 【core   】     Convert工具类中，新增中文大写数字金额转换为数字工具方法（pr#674@Gitee）
+* 【core   】     新增CollectorUtil.reduceListMap()（pr#676@Gitee）
 * 
 ### 🐞Bug修复
 

hutool-core/src/main/java/cn/hutool/core/stream/CollectorUtil.java

@@ -3,12 +3,13 @@ package cn.hutool.core.stream;
 import cn.hutool.core.lang.Opt;
 import cn.hutool.core.util.StrUtil;
 
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.List;
 import java.util.StringJoiner;
 import java.util.function.BiConsumer;
 import java.util.function.BinaryOperator;
@@ -99,26 +100,23 @@ public class CollectorUtil {
 	public static <T, K, D, A, M extends Map<K, D>> Collector<T, ?, M> groupingBy(Function<? super T, ? extends K> classifier,
 																				  Supplier<M> mapFactory,
 																				  Collector<? super T, A, D> downstream) {
-		Supplier<A> downstreamSupplier = downstream.supplier();
+		final Supplier<A> downstreamSupplier = downstream.supplier();
-		BiConsumer<A, ? super T> downstreamAccumulator = downstream.accumulator();
+		final BiConsumer<A, ? super T> downstreamAccumulator = downstream.accumulator();
-		BiConsumer<Map<K, A>, T> accumulator = (m, t) -> {
+		final BiConsumer<Map<K, A>, T> accumulator = (m, t) -> {
-			K key = Opt.ofNullable(t).map(classifier).orElse(null);
+			final K key = Opt.ofNullable(t).map(classifier).orElse(null);
-			A container = m.computeIfAbsent(key, k -> downstreamSupplier.get());
+			final A container = m.computeIfAbsent(key, k -> downstreamSupplier.get());
 			downstreamAccumulator.accept(container, t);
 		};
-		BinaryOperator<Map<K, A>> merger = mapMerger(downstream.combiner());
+		final BinaryOperator<Map<K, A>> merger = mapMerger(downstream.combiner());
-		@SuppressWarnings("unchecked")
+		@SuppressWarnings("unchecked") final Supplier<Map<K, A>> mangledFactory = (Supplier<Map<K, A>>) mapFactory;
-		Supplier<Map<K, A>> mangledFactory = (Supplier<Map<K, A>>) mapFactory;
 
 		if (downstream.characteristics().contains(Collector.Characteristics.IDENTITY_FINISH)) {
 			return new SimpleCollector<>(mangledFactory, accumulator, merger, CH_ID);
 		} else {
-			@SuppressWarnings("unchecked")
+			@SuppressWarnings("unchecked") final Function<A, A> downstreamFinisher = (Function<A, A>) downstream.finisher();
-			Function<A, A> downstreamFinisher = (Function<A, A>) downstream.finisher();
+			final Function<Map<K, A>, M> finisher = intermediate -> {
-			Function<Map<K, A>, M> finisher = intermediate -> {
 				intermediate.replaceAll((k, v) -> downstreamFinisher.apply(v));
-				@SuppressWarnings("unchecked")
+				@SuppressWarnings("unchecked") final M castResult = (M) intermediate;
-				M castResult = (M) intermediate;
 				return castResult;
 			};
 			return new SimpleCollector<>(mangledFactory, accumulator, merger, finisher, CH_NOID);
@@ -214,5 +212,40 @@ public class CollectorUtil {
 		};
 	}
 
+	/**
+	 * 聚合这种数据类型:{@code Collection<Map<K,V>> => Map<K,List<V>>}
+	 * 其中key相同的value，会累加到List中
+	 *
+	 * @param <K> key的类型
+	 * @param <V> value的类型
+	 * @return 聚合后的map
+	 * @since 5.8.5
+	 */
+	public static <K, V> Collector<Map<K, V>, ?, Map<K, List<V>>> reduceListMap() {
+		return reduceListMap(HashMap::new);
+	}
+
+	/**
+	 * 聚合这种数据类型:{@code Collection<Map<K,V>> => Map<K,List<V>>}
+	 * 其中key相同的value，会累加到List中
+	 *
+	 * @param mapSupplier 可自定义map的类型如concurrentHashMap等
+	 * @param <K>         key的类型
+	 * @param <V>         value的类型
+	 * @param <R>         返回值的类型
+	 * @return 聚合后的map
+	 * @since 5.8.5
+	 */
+	public static <K, V, R extends Map<K, List<V>>> Collector<Map<K, V>, ?, R> reduceListMap(final Supplier<R> mapSupplier) {
+		return Collectors.reducing(mapSupplier.get(), value -> {
+					final R result = mapSupplier.get();
+					value.forEach((k, v) -> result.computeIfAbsent(k, i -> new ArrayList<>()).add(v));
+					return result;
+				}, (l, r) -> {
+					r.forEach((k, v) -> l.computeIfAbsent(k, i -> new ArrayList<>()).addAll(v));
+					return l;
+				}
+		);
+	}
 
 }

hutool-core/src/test/java/cn/hutool/core/stream/CollectorUtilTest.java

@@ -0,0 +1,30 @@
+package cn.hutool.core.stream;
+
+import cn.hutool.core.map.MapUtil;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+public class CollectorUtilTest {
+	@Test
+	public void reduceListMapTest() {
+		final Set<Map<String, Integer>> nameScoreMapList = StreamUtil.of(
+				// 集合内的第一个map，包含两个key value
+				MapUtil.builder("苏格拉底", 1).put("特拉叙马霍斯", 3).build(),
+				MapUtil.of("苏格拉底", 2),
+				MapUtil.of("特拉叙马霍斯", 1),
+				MapUtil.of("特拉叙马霍斯", 2)
+		).collect(Collectors.toSet());
+		// 执行聚合
+		final Map<String, List<Integer>> nameScoresMap = nameScoreMapList.stream().collect(CollectorUtil.reduceListMap());
+
+		Assert.assertEquals(MapUtil.builder("苏格拉底", Arrays.asList(1, 2))
+						.put("特拉叙马霍斯", Arrays.asList(3, 1, 2)).build(),
+				nameScoresMap);
+	}
+}