在Java 8中将List <CustomObject1>转换为Map <CustomObject2，Set <CustomObject2>

问题描述

解析文件后，我得到了CustomObject1的列表。 CustomObject1如下。

class CustomObject1{

  List<CustomObject2> type;
  List<CustomObject2> mapping;
}

class CustomObject2 {

  String name;
  String surname;
}

CustomObject1的列表示例就像

CustomObject2 obj1 = new CustomObject2();
CustomObject2 obj2 = new CustomObject2();

CustomObject2 type1 = new CustomObject2();
CustomObject2 type2 = new CustomObject2();

CustomObject1 listofObj1 = new CustomObject1(List.of(type1,type2),List.of(obj1,obj2));

另一个CustomObject实例

CustomObject2 obj3 = new CustomObject2();
CustomObject2 obj4 = new CustomObject2();

CustomObject2 type3 = new CustomObject2();
CustomObject2 type4 = new CustomObject2();

//Existing ** type1 ** has another mapping
 CustomObject1 listofObj2 = new CustomObject1(List.of(type1,type3,type4),List.of(obj3,obj4));


//Final list of CustomObject1 that we need to convert is 
List<CustomObject1> finalList = List.of(listofObj1,listofObj2);

预期的输出就像

{type1 = [obj1，obj2，obj3，obj4]，type2 = [obj1，obj2]，type3 = [obj3，obj4]，type4 = [obj3，obj4]}

我用以下代码实现了映射

Map<CustomObject2,Set<CustomObject2>> finalMapping = new HashMap<>();

      finalList.forEach(listItem-> listItem.getType().forEach(type -> {
            if (!finalMapping.containsKey(type)) {
              finalMapping.put(type,Set.copyOf(listItem.getMapping()));
            } else {
              Set<CustomObject2> combined = concat(finalMapping.get(type).stream(),listItem.getMapping().stream())
                  .collect(toSet());
              finalMapping.put(type,combined);
            }
          }
      ));

是否有任何方法可以在Java 8中使用lamda实现到Map 的转换。

解决方法

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java-8 java-stream