Java 8并行流并发分组 [英] Java 8 Parallel Stream Concurrent Grouping

问题描述

假设我有一个类

Class Person {
  String name;
  String uid;
  String phone;
}

我正在尝试按类的所有字段进行分组。如何在JAVA 8中使用并行流来转换

I am trying to group by all the fields of the class. How do i use parallel streams in JAVA 8 to convert a

List<Person> into Map<String,Set<Person>>

其中地图的关键字是类中每个字段的值。 JAVA 8以下示例分组由单个字段组成，如何将一个类的所有字段组成一个映射？

where the key of the map is the value of each field in the class . JAVA 8 the following example groups by a single field, how can i do it for all fields of a class into a single Map?

ConcurrentMap<Person.Sex, List<Person>> byGender =
roster
    .parallelStream()
    .collect(
        Collectors.groupingByConcurrent(Person::getGender));

推荐答案

你可以使用<$ c $来做到这一点c> of 来自收集器的静态工厂方法：

Map<String, Set<Person>> groupBy = persons.parallelStream()
    .collect(Collector.of(
        ConcurrentHashMap::new,
        ( map, person ) -> {
            map.computeIfAbsent(person.name, k -> new HashSet<>()).add(person);
            map.computeIfAbsent(person.uid, k -> new HashSet<>()).add(person);
            map.computeIfAbsent(person.phone, k -> new HashSet<>()).add(person);
        },
        ( a, b ) -> {
            b.forEach(( key, set ) -> a.computeIfAbsent(key, k -> new HashSet<>()).addAll(set));
            return a;
        }
    ));

正如评论中提到的Holger，以下方法可以优先于上述方法：

As Holger in the comments suggested, following approach can be preffered over the above one:

Map<String, Set<Person>> groupBy = persons.parallelStream()
     .collect(HashMap::new, (m, p) -> { 
         m.computeIfAbsent(p.name, k -> new HashSet<>()).add(p); 
         m.computeIfAbsent(p.uid, k -> new HashSet<>()).add(p); 
         m.computeIfAbsent(p.phone, k -> new HashSet<>()).add(p); 
     }, (a, b) -> b.forEach((key, set) -> {
         a.computeIfAbsent(key, k -> new HashSet<>()).addAll(set));
     });

它使用重载的 collect 方法与我上面建议的陈述相同。

It uses the overloaded collect method which acts identical to my suggested statement above.

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