jdk8中list集合二次分组
场景：首先针对同一个城市的人进行分组，在此基础上再对年龄进行分组。
Student实体类如下：
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class Student{
private String city;
private String age;
private String name;
}
测试类如下：
@Test
public void test(){
//测试数据如下
Student build1 = Student.builder().city("新疆").age("88").name("李四").build();
Student build2 = Student.builder().city("哈尔滨").age("45").name("王五").build();
Student build3 = Student.builder().city("哈尔滨").age("23").name("借口").build();
Student build4 = Student.builder().city("广东").age("33").name("刺刀").build();
Student build6 = Student.builder().city("广东").age("18").name("张三").build();
Student build7 = Student.builder().city("广东").age("23").name("士大夫").build();
Student build5 = Student.builder().city("南京").age("188").name("宽带").build();
List<Student> students = Arrays.asList(build1, build2, build3, build4, build5, build6, build7);
//在根据城市进行分组的条件下，在对相同年龄的学生进行二次分组
Map<String, Map<String, List<Student>>> collect = students.parallelStream().collect(Collectors.groupingBy(Student::getCity, Collectors.groupingBy(Student::getAge)));
Set<Map.Entry<String, Map<String, List<Student>>>> entries = collect.entrySet();
for (Map.Entry<String, Map<String, List<Student>>> ele: entries) {
Map<String, List<Student>> subEle = ele.getValue();
Set<Map.Entry<String, List<Student>>> entrySet = subEle.entrySet();
for (Map.Entry<String, List<Student>> realEle: entrySet) {
System.out.println(realEle);
}
}
}
测试结果：
场景：首先针对同一个城市的人进行分组，在此基础上再对年龄进行分组。 Student实体类如下： @Data @Builder @NoArgsConstructor @AllArgsConstructor public class Student{ private String city; private String age; private String name; } 测试类如下： @Test public void test(){ //测试数据如下 Student build1 = Student.builder().city("新疆").age("88").name("李四").build(); Student build2 = Student.builder().city("哈尔滨").age("45").name("王五").build(); Student build3 = Student.builder().city("哈尔滨").age("23").name("借口").build(); Student build4 = Student.builder().city("广东").age("33").name("刺刀").build(); Student build6 = Student.builder().city("广东").age("18").name("张三").build(); Student build7 = Student.builder().city("广东").age("23").name("士大夫").build(); Student build5 = Student.builder().city("南京").age("188").name("宽带").build(); List