[英]java 8 stream groupingBy into collection of custom object
I have the following class structure我有以下类结构
public class Store {
private Long storeId;
private Long masterStoreId;
private String operatorIdentifier;
}
public class StoreInfo {
private String operatorIdentifier;
private Set<Long> slaveStoreIds;
public StoreInfo(String operatorIdentifier, Set<Long> slaveStoreIds) {
super();
this.operatorIdentifier = operatorIdentifier;
this.slaveStoreIds = slaveStoreIds;
}
}
I want to collect the "List<Store" into a "Map<Long, StoreInfo>".我想将“List<Store”收集到“Map<Long, StoreInfo>”中。 Is it possible to do so in a single operation/iteration?
是否可以在单个操作/迭代中这样做?
List<Store> stores;
Map<Long, Set<Long>> slaveStoresAgainstMasterStore = stores.stream().collect(Collectors
.groupingBy(Store::getMasterStoreId, Collectors.mapping(Store::getStoreId, Collectors.toSet())));
Map<Long, StoreInfo> storeInfoAgainstMasterStore = stores.stream()
.collect(
Collectors
.toMap(Store::getMasterStoreId,
val -> new StoreInfo(val.getOperatorIdentifier(),
slaveStoresAgainstMasterStore.get(val.getMasterStoreId())),
(a1, a2) -> a1));
As masterStoreId
and operatorIdentifier
are same same in group(comfirmed in comment) you can groupingBy both creating pair of them using AbstractMap.SimpleEntry
.由于
masterStoreId
和operatorIdentifier
在组中相同(在评论中确认),您可以 groupingBy 使用AbstractMap.SimpleEntry
创建它们对。 Then using Collectors.toMap
create map.然后使用
Collectors.toMap
创建地图。
Map<Long, StoreInfo> storeInfoMap =
stores.stream()
.collect(Collectors.groupingBy(
e -> new AbstractMap.SimpleEntry<>(e.getMasterStoreId(),
e.getOperatorIdentifier()),
Collectors.mapping(Store::getStoreId, Collectors.toSet())))
.entrySet()
.stream()
.collect(Collectors.toMap(e -> e.getKey().getKey(),
e -> new StoreInfo(e.getKey().getValue(), e.getValue())));
To complete the implementation, you were attempting.为了完成实施,您正在尝试。 You need to ensure merging capability within
StoreInfo
such as :您需要确保
StoreInfo
合并功能,例如:
public StoreInfo(String operatorIdentifier, Long slaveStoreId) {
this.operatorIdentifier = operatorIdentifier;
this.slaveStoreIds = new HashSet<>();
this.slaveStoreIds.add(slaveStoreId);
}
public static StoreInfo mergeStoreInfo(StoreInfo storeInfo1, StoreInfo storeInfo2) {
Set<Long> slaveIds = storeInfo1.getSlaveStoreIds();
slaveIds.addAll(storeInfo2.getSlaveStoreIds());
return new StoreInfo(storeInfo1.getOperatorIdentifier(), slaveIds);
}
this would simplify the implementation of collector and you an invoke these correspondingly:这将简化收集器的实现,您可以相应地调用这些:
Map<Long, StoreInfo> storeInfoAgainstMasterStore = stores.stream()
.collect(Collectors.toMap(Store::getMasterStoreId,
store -> new StoreInfo(store.getOperatorIdentifier(), store.getStoreId()),
StoreInfo::mergeStoreInfo));
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.