hutool修复CollectorUtil.reduceListMap与Collectors.groupby一起使用时出现与预期不符的结果
待小人宜宽，防小人宜严。——金瑛
问题的
issue
：
https://github.com/dromara/hutool/issues/3380
此处复现：
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);
// 期望数据
// {jack={name=[jack, jack], count=[80, 90]}, sam={name=[sam, sam, sam], count=[80, 81, 82]}}
// 实际数据
// {jack={name=[sam, sam, sam, jack, jack], count=[80, 81, 82, 80, 90]}, sam={name=[sam, sam, sam, jack, jack], count=[80, 81, 82, 80, 90]}}
原因是在
reducing
的第三个参数里出现重复引用导致问题
解决办法：每次都调用第一个参数的
supplier
创建新
map
将原来的：
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;
}改为：
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) -> {
final R resultMap = mapSupplier.get();