[英]Java8 group a list of lists to map
I have a Model
and a Property
class with the following signatures: 我有一个
Model
和一个带有以下签名的Property
类:
public class Property {
public String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
public class Model {
private List<Property> properties = new ArrayList<>();
public List<Property> getProperties() {
return properties;
}
}
I want a Map<String, Set<Model>>
from a List<Model>
where the key would be the name from the Property
class. 我想从
List<Model>
中Map<String, Set<Model>>
,其中键是Property
类中的名称。 How can I can I use java8 streams to group that list by its Propery
es' name? 我怎样才能使用java8流按其
Propery
es'名称对该列表进行Propery
? All Property
es are unique by name. 所有
Property
都是名称唯一的。
It is possible to solve in a single stream or should I split it somehow or go for the classical solution? 可以在单个流中解决,还是应该以某种方式拆分它或者寻找经典的解决方案?
yourModels.stream()
.flatMap(model -> model.getProperties().stream()
.map(property -> new AbstractMap.SimpleEntry<>(model, property.getName())))
.collect(Collectors.groupingBy(
Entry::getValue,
Collectors.mapping(
Entry::getKey,
Collectors.toSet())));
Why not use forEach
? 为什么不使用
forEach
?
Here is concise solution using forEach
这是使用
forEach
简洁解决方案
Map<String, Set<Model>> resultMap = new HashMap<>();
listOfModels.forEach(currentModel ->
currentModel.getProperties().forEach(prop -> {
Set<Model> setOfModels = resultMap.getOrDefault(prop.getName(), new HashSet<>());
setOfModels.add(currentModel);
resultMap.put(prop.getName(), setOfModels);
})
);
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