Java8分组要映射的列表列表 [英] Java8 group a list of lists to map

问题描述

我有一个 Model 和一个具有以下签名的 Property 类:

I have a Model and a Property class with the following signatures:

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;
    }
}

我想要 List<Model> 中的 Map<String, Set<Model>>，其中键是 Property<中的名称/代码>类.如何使用 java8 流按其 Properyes 名称对该列表进行分组?所有 Property 的名称都是唯一的.

I want a Map<String, Set<Model>> from a List<Model> where the key would be the name from the Property class. How can I can I use java8 streams to group that list by its Properyes' name? All Propertyes are unique by name.

可以在单个流中解决，还是应该以某种方式拆分它还是采用经典解决方案?

It is possible to solve in a single stream or should I split it somehow or go for the classical solution?

推荐答案

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())));

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