Java8 stream groupingBy 多字段分组

南来北往的客

于 2019-03-08 09:28:15 发布

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分类专栏： JDK8 文章标签： Java8 Java8 stream groupingBy

本文链接：https://blog.youkuaiyun.com/xlb744868186/article/details/88327395

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本文深入探讨了 Java Stream API 的高级应用，通过实例演示如何使用 Stream 对 List 中的数据进行分组与聚合操作，展示了如何将学生列表按姓名分组，以及进一步按性别分组的过程。

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public class Test {
    public static void main(String[] args) {
        List<Student> students = new ArrayList<Student>();
        Student student = new Student("张三","女","11");
        Student student2 = new Student("张三","男","11");
        Student student3 = new Student("张三","男","11");
        Student student4 = new Student("李四","男","11");
        Student student5 = new Student("李四","男","11");
        Student student6 = new Student("王五","男","11");
        students.add(student);
        students.add(student2);
        students.add(student3);
        students.add(student4);
        students.add(student5);
        students.add(student6);
        Map<String,List<Student>> map = students.stream().collect(Collectors.groupingBy(Student :: getName));
        map.forEach((k,v) -> {
            System.out.println("k = "+ k + "||" +"v = " + v.stream().collect(Collectors.groupingBy(Student :: getSex)).size());
        });

    }
}

        Map<List<String>, List<Student>> map = students.stream()
                .collect(Collectors.groupingBy(f -> Arrays.asList(f.getName(),f.getSex())));

        map.forEach((o, o2) -> {
            List<Student> studentss = o2;
            studentss.forEach(s -> System.out.println(s.getName()));
        });