如何构造复杂map

数据库中有一组学生
如何构造出这么一个Map集合  Map>>
第一个String 是性别
第二个String 是年龄就是先从数据库里面查询出来

如何构造出这样的集合

普通写法：

Map>> resultMap = new HashMap<>();
Map> sexMap = new HashMap<>();
            for (Student student : students) {
                List tempList = sexMap.get(student.getSex());
                if (tempList == null) {
                    tempList = new ArrayList<>();
                    tempList.add(student);

                }
                else {
                    tempList.add(student);
                }
                sexMap.put(student.getSex(), tempList);
            }
            System.out.println(sexMap);

            for (Map.Entry> entry : sexMap.entrySet()) {
                String key = entry.getKey().toString();//sex
                List value = entry.getValue();
                System.out.println("key=" + key + " value=" + value);
                Map> ageMap = new HashMap<>();
                for (Student student : value) {
                    List tempList = ageMap.get(student.getAge());
                    if (tempList == null) {
                        tempList = new ArrayList<>();
                        tempList.add(student);

                    }
                    else {
                        tempList.add(student);
                    }
                    ageMap.put(student.getAge(), tempList);
                    resultMap.put(key,ageMap);
                }

            }
            System.out.println(resultMap);

java8写法：

Map>> resultMap = new HashMap<>();
Map> sexMap = students.stream().collect(Collectors.groupingBy(Student::getSex));
sexMap.entrySet().forEach(entry -> resultMap.put(entry.getKey(),entry.getValue().stream().collect(Collectors.groupingBy(Student::getAge))));