list<object> to list<Map>, and a certain field as the key value value

       List<User> list = new ArrayList<>();
        list.add(new Student("男", "zhangsan"));
        list.add(new Student("男", "lisi"));
        Map<String, Object> result = list.stream().collect(Collectors.toMap( user -> {
    
    
            return (String)user.getSex();
        }, User::getName));