Java 8 lambda Stream list to Map key 重复 value合并到Collection

2024年1月1日 3,923次阅读来源: feiwuguohai

List<String> list = Lists.newArrayList(“1”, “2”, “3”, “1”);
Map<String, List<String>> map = list.stream().collect(Collectors.toMap(key -> key,
value -> Lists.newArrayList(value),
(List<String> newValueList, List<String> oldValueList) -> {
oldValueList.addAll(newValueList);
return oldValueList;
}));
System.out.println(JSON.toJSONString(map));

Map<String,List<Parts>> partsMap = partList.stream().collect(Collectors.toMap(Parts::getMaintainCode, part ->
Lists.newArrayList(part),(List<Parts> newValueList,List<Parts> oldValueList)->
{oldValueList.addAll(newValueList);
return oldValueList;
}));

    原文作者：feiwuguohai
    原文地址: https://blog.csdn.net/feiwuguohai/article/details/80522998
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