Java：将 Object 列表转换为另一个 hashmap 内部的 ZDDA7806A48467A51B5940AAABZ

Question

我有一个要转换为 hash map 的对象列表。 是否可以创建这种类型的哈希映射Map<String, Map<String, List<Object>> ？

这样做的原因是我需要按对象中的某些属性对它们进行排序，以便以后可以遍历它。 下面是 Json 对象当前的样子：

[
  object1: {plan: "11", relationship: "A", etc...},
  object2: {plan: "12", relationship: "A", etc...},
  object3: {plan: "11", relationship: "B", etc...},
]

I was trying to use Collectors to get it into a HashMap but i am confused on the second hash map, I can't seem to get the list of relationships into a Map .

Map<String, Map<String, List<myObject>> myHash = objectList
    .stream()
    .collect(Collectors.toMap(myObject::plan, 
        a -> a.stream().collect(Collectors.groupingBy(myObject::relationship))));

我想得到的是这样的

[
  {
    key: "11", 
    value: [
             {key: "A", value: [ object1 ]},
             {key: "B", value: [ object3 ]}
           ]
  },
  {
    key: "12",
    value: [{key: "A", value: [ object2 ]}]
  }
]

Answer 1

您可以分组两次，“关系”分组收集器是“计划”分组收集器的下游：

Map<String, Map<String, List<myObject>> myHash = objectList
    .stream()
    .collect(Collectors.groupingBy(myObject::getPlan, 
                Collectors.groupingBy(myObject::getRelationship)));

这将使每个“计划”组下的“关系”组。