流式计算知识

对象属性为数组，根据属性分组统计

数据结构：

[
{
    "id":"1","name":["aa","bb"]},
{
    "id":"1","name":["bb","cc"]}
]

需求：我们需要将name里面的属性值进行分组统计个数
方法一：

  ArrayList<Person> peoples = new ArrayList<>();
        peoples.add(new Person("1", Stream.of("aa", "bb").collect(Collectors.toList())));
        peoples.add(new Person("2", Stream.of("bb", "cc").collect(Collectors.toList())));
        Map<String, Integer> collect = peoples.stream().flatMap(people -> people.getName().stream()).collect(Collectors.toMap(k -> k, v -> 1, Integer::sum));
        System.out.println(collect);

方法二：

HashMap<String, Integer> map = new HashMap<>();
        ArrayList<Person> peoples = new ArrayList<>();
        peoples.add(new Person("1", Stream.of("aa", "bb").collect(Collectors.toList())));
        peoples.add(new Person("2", Stream.of("bb", "cc").collect(Collectors.toList())));
        peoples.stream().flatMap(people -> people.getName().stream()).forEach(str -> map.merge(str, 1, Integer::sum));
        map.forEach((k, v) -> System.out.println(k + " " + v));