[Fix] 修复 github issue 3380 CollectorUtil.reduceListMap与collectors.groupby一起使用时出现与预期不符的结果

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

@@ -243,8 +243,13 @@ public class CollectorUtil {
 					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;
+					R resultMap = mapSupplier.get();
+					resultMap.putAll(l);
+					r.forEach((k, v) -> {
+						List<V> list = resultMap.computeIfAbsent(k, i -> new ArrayList<>());
+						list.addAll(v);
+					});
+					return resultMap;
 				}
 		);
 	}

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

@@ -1,5 +1,6 @@
 package cn.hutool.core.stream;
 
+import cn.hutool.core.collection.ListUtil;
 import cn.hutool.core.map.MapUtil;
 import org.junit.Assert;
 import org.junit.Test;
@@ -29,6 +30,22 @@ public class CollectorUtilTest {
 		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);
+
+		List<Map<String, String>> data = ListUtil.toList(
+			MapUtil.builder("name", "sam").put("count", "80").map(),
+			MapUtil.builder("name", "sam").put("count", "81").map(),
+			MapUtil.builder("name", "sam").put("count", "82").map(),
+			MapUtil.builder("name", "jack").put("count", "80").map(),
+			MapUtil.builder("name", "jack").put("count", "90").map()
+		);
+
+		Map<String, Map<String, List<String>>> nameMap = data.stream()
+			.collect(Collectors.groupingBy(e -> e.get("name"), CollectorUtil.reduceListMap()));
+		Assert.assertEquals(MapUtil.builder("jack", MapUtil.builder("name", Arrays.asList("jack", "jack"))
+				.put("count", Arrays.asList("80", "90")).build())
+			.put("sam", MapUtil.builder("name", Arrays.asList("sam", "sam", "sam"))
+				.put("count", Arrays.asList("80", "81", "82")).build())
+			.build(), nameMap);
 	}
 
 	@Test