java8 分组排序_java8分组排序-优快云博客

本文链接：https://blog.youkuaiyun.com/qiqin5978/article/details/115866987

本文介绍了一种使用Java实现的多字段分组及排序的方法。通过自定义内部类来存储分组依据，并利用Stream API结合Comparator进行复杂的数据处理。具体展示了如何创建一个Student类及其内部类Mid用于分组，最后通过测试用例验证了分组和排序功能。

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多字段分组并按分组字段进行排序

将分组字段定义为内部类的属性，并增加方法getMid()
测试

将分组字段定义为内部类的属性，并增加方法getMid()

@Data
public class Student {
    private String name;
    private int grade;
    private Date time;
    private int age;


    @Data
    public class Mid {
        private int grade;
        private Date time;

        public Mid(int grade, Date time) {
            this.grade = grade;
            this.time = time;
        }
    }

    public Mid getMid() {
        return new Mid(grade, time);
    }
}

测试

@Test
    void testGroup() {
        List<Student> list = new ArrayList<>();
        Random r = new Random(3);
        for (int i = 0; i < 10; i++) {
            Student s = new Student();
            int grade = r.nextInt(5);
            Date time = new Date();
            long now = time.getTime() - grade * 10000;
            time.setTime(now);
            s.setTime(time);
            s.setGrade(grade);
            s.setAge(i);
            s.setName("Tom" + i);
            list.add(s);

        }
        for (Student student : list) {
            System.out.println("_____________");
            System.out.println(student.getName());
            System.out.println(student.getAge());
            System.out.println(student.getGrade());
            System.out.println(new SimpleDateFormat("yyyy-MM-dd HH:ss:mm").format(student.getTime()));
        }

        TreeMap<Student.Mid, List<Student>> collect = list.stream()
                .sorted(Comparator.comparing(Student::getAge).reversed())
                .collect(Collectors.groupingBy(Student::getMid,
                        () -> new TreeMap<>((a, b) -> {
                            if (a.toString().equals(b.toString())) {
                                return 0;
                            }
                            else{
                                if (a.getTime().before(b.getTime())) {
                                    return 1;
                                }
                                return -1;
                            }
                        }),
                        Collectors.toList()
                ));

    }