我提出了这个问题:使用forEach和Java 8创建嵌套列表(List of List)的流
。class EntityCompositeId {
private Long firstId;
private Long secondId;
// getter & setter...
}
class EntityComposite {
private EntityCompositeId id;
private String first;
private String second;
// getter & setter...
}
List<EntityComposite> listEntityComposite = ....
Supose this content
1, 1, "firstA", "secondBirdOne"
1, 2, "firstA", "secondBirdTwo"
1, 3, "firstA", "secondBirdThree"
2, 1, "firstB", "secondCatOne"
2, 2, "firstB", "secondCatTwo"
2, 3, "firstB", "secondCatThree"
3, 1, "firstC", "secondDogOne"
3, 2, "firstC", "secondDogTwo"
3, 3, "firstC", "secondDogThree"
Map<Long, Map<Long, String>> listOfLists = new HashMap<>();
现在我想使用流来填充,例如:
1 -> {1 ->"secondBirdOne", 2 -> "secondBirdTwo", 3 -> "secondBirdThree"}
2 -> {1 ->"secondCatOne", 2 -> "secondCatTwo", 3 -> "secondCatThree"}
3 -> {1 ->"secondDogOne", 2 -> "secondDogTwo", 3 -> "secondDogThree"}
我的代码没有起作用,代码如下:
Map<Long, Map<Long, String>> listaMunDepa = listEntityComposite.stream()
.collect(Collectors.groupingBy(
e -> e.getId().getFirstId(),
Collectors.toMap(f -> f.getId().getSecondId(), Function.identity()))
);
第二次尝试
Map<Long, Map<Long, String>> listaMunDepa = listEntityComposite.stream()
.collect(Collectors.groupingBy(
e -> e.getId().getFirstId(),
Collectors.groupingBy(EntityComposite::getId::getSecondId, EntityComposite::getSecond)) // How change this line
);