Streams Java8: Group by Sum

 public static void groupingByMapSum(){

    User user =new User();
    user.setId(1);
    user.setName("test");
    List<User> users =new ArrayList<>();
    users.add(user);
    user =new User();
    user.setId(1);
    user.setName("test1");
    users.add(user);

    Map<Integer,Integer> params=
            users.stream().collect(Collectors.groupingBy(User::getId,
                    Collectors.summingInt(e->1)));

    System.out.println(params);
}