[英]get list of ids from list of objects from inner list java 8
I have list of entity class: 我有实体类的列表:
public class Entity
{
private long id;
private List<InnerEnity> data;
public long getId() {
return id;
}
public List<InnerEnity> getData() {
return data;
}
}
this is InnerEnity class 这是InnerEnity类
public class InnerEnity
{
private long id;
private String data;
public long getId() {
return id;
}
public String getData() {
return data;
}
}
what i need is list of InnerEnity ids. 我需要的是InnerEnity ID列表。 to resolve this i am trying something like that :-
为了解决这个问题,我正在尝试类似的东西:
List innerEnityIds = listOfEnity.stream().map(sys -> sys.getData().stream().map(obj->obj.getId().collect(Collectors.toList())));
Here you need flatMap
: 在这里,您需要
flatMap
:
List<Long> innerEnityIds =
listOfEnity.stream() // Stream<Entity>
.flatMap(sys -> sys.getData().stream().map(InnerEntity::getId)) // Stream<Long>
.collect(Collectors.toList()); // List<Long>
Or, you can break the flatMap
step into flatMap
+ map
: 或者,您可以将
flatMap
步骤分解为flatMap
+ map
:
List<Long> innerEnityIds =
listOfEnity.stream() // Stream<Entity>
.flatMap(sys -> sys.getData().stream()) // Stream<InnerEntity>
.map(InnerEntity::getId) // Stream<Long>
.collect(Collectors.toList()); // List<Long>
I think this might do the trick (haven't tested it): 我认为这可能会解决问题(尚未测试):
List<Long> innerEntityIds = listOfEnity.stream()
.flatMap(e -> e.getData().stream()) // 1
.map(ie -> ie.getId()) // 2
.collect(Collectors.toList()); // 3
1) stream all the inner entities into one stream using flatMap 2) map each inner entity to its id 3) collect the id's into a list 1)使用flatMap将所有内部实体串流到一个流中2)将每个内部实体映射到其ID 3)将ID收集到一个列表中
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