如何将 java 对象列表转换为 Map<String、Map<String、String>>

Question

我有一个java对象列表，如下所示：

[
{
id: "frwfhfijvfhviufhbviufg",
country_code: "DE",
message_key: "key1",
translation: "This is the deutsch translation"
},
{
id: "dfregregtegetgetgttegt",
country_code: "GB",
message_key: "key1",
translation: "This is the uk translation"
},
{
id: "frffgfbgbgbgbgbgbgbgbg",
country_code: "DE",
message_key: "key2",
translation: "This is the again deutch translation"
}
]

如何将其转换为Map<String, Map<String, String>>，如下所示：

{
"DE": {
"key1": "This is the deutsch translation",
"key2": "This is the again deutch translation"
},
"GB": {
"key1": "This is the uk translation"
}
}

我是java新手，下面是我的代码，但代码不正确：

Map<String, Translations> distinctTranslations = customTranslationsEntities
.stream().collect(Collectors.groupingBy(
CustomTranslationsEntity::getCountryCode,
Collectors.toMap(
CustomTranslationsEntity::getMessageKey,
CustomTranslationsEntity::getTranslation),
)))

其中Translations是如下所示的原型缓冲区消息：

message Translations {
map<string, string> translations = 1;
}

这里map<string, string> translations的意思是类似于"key1", "This is the deutsch translation"的映射。。。像这样。

Answer 1

输出应为Map<String, Map<String,String>>:

Map<String, Map<String,String>>
distinctTranslations = customTranslationsEntities
.stream()
.collect(Collectors.groupingBy(CustomTranslationsEntity::getCountryCode,
Collectors.toMap(
CustomTranslationsEntity::getMessageKey,
CustomTranslationsEntity::getTranslation,
(v1,v2)->v1)));

我添加了一个合并功能，以防出现重复的键。

Answer 2

如果你想在不使用流的情况下完成，那么

private List<MyObject> list = // Your object List
private Map<String, Map<String, String>> map = new HashMap<>();
for(MyObject object : list){
Map<String, String> localMap;
localMap = map.getOrDefault(object.country_code, new HashMap<>());
localMap.put(object.message_key, object.translation);
if(!map.containsKey(object.country_code)){
map.put(object.country_code, localMap);
}
}