add method

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);
+	}
+}