普通对象列表进行分组

// 创建一个实体类
@Data
public class People {String name;    //姓名Integer age;    //年龄Integer sex;     //性别   0 - 女； 1 - 男Double height;  //身高Double weight;  //体重
}public class ListGroupTest {public static void main(String[] args) {List<People> list = new ArrayList<>();Random random = new Random();for (int i = 0; i < 10; i++) {People people = new People();people.setName("name" + i);people.setAge(random.nextInt(50));people.setSex(random.nextInt(1));people.setHeight(random.nextDouble());people.setWeight(random.nextDouble());list.add(people);}//根据性别分组Map<Integer, List<People>> collect = list.stream().collect(Collectors.groupingBy(People::getSex));}
}

map或jsonObject 列表进行分组

//list准备Map map1 = new HashMap();map1.put("schoolId",1);map1.put("gradeId",1);map1.put("city",1);Map map2 = new HashMap();map2.put("schoolId",2);map2.put("gradeId",2);map2.put("city",2);Map map5 = new HashMap();map5.put("schoolId",3);map5.put("gradeId",3);map5.put("city",3);List<Map> list1 = new ArrayList<>();list1.add(map1);list1.add(map2);list1.add(map5);//根据schoolId进行分组
Map<Object, List<Map>> mapGroup1 = list1.stream().collect(Collectors.groupingBy(o -> o.get("schoolId")));//根据schoolId和gradeId进行分组
Map<String, List<Map>> mapGroup2 = list1.stream().collect(Collectors.groupingBy(o -> "-"+o.get("schoolId")+ '-' + o.get("gradeId")));List<String> paramsList = new ArrayList();
paramsList.add("schoolId");
paramsList.add("gradeId");
paramsList.add("city");
//多字段进行分组	(StringUtils.join将列表拼接为字符串返回)
Map<String, List<Map>> mapGroup3 = list1.stream().collect(Collectors.groupingBy(o -> StringUtils.join(paramsList.stream().map(key -> "-" + o.get(key)).collect(Collectors.toList()), "")));