## Retrieving unique user data in Spring Security

[Source](http://stackoverflow.com/questions/9716442/retrieving-unique-user-data-in-spring-security)

I have a table of items, user should be able to choose some of them, then these items 
are put in the other table (in the second table they are associated with the user who 
chose the items). I could associate items and users with a help of usernames, but 
I suppose it wouldn't be great. I wonder, what is a good way to do that.

I know there is an easy way to retrieve the username 
(`<sec:authentication property="principal.username"/>`), but today I learnt there is 
no such a way for an id. 

* What is a good way to solve this problem? 
* Should I implement UserDetails to have an opportunity to get each id? 
* Is there any good example of this implementation? I use Hibernate to 
  communicate with the database. 
* Is there any other way of the identification (compound key consisted of values that 
are easy to retrieve or something like that)? 


### Answer

Yes you have to implement your own UserDetail which will have an id attribute.

You'll then fill in this object during authentication in your implementation of UserDetailService.

For example:

~~~~
@Service("CustomUserDetailService")
public class CustomUserDetailService implements UserDetailsService{

    @Autowired
    private IUserDao userDao;

    @Override
    public UserDetails loadUserByUsername(String name) 
                                          throws UsernameNotFoundException, 
                                                 DataAccessException {
        User user = userDao.loadByName(name);
        CustomUserDetail customUserDetail = new CustomUserDetail();
        customUserDetail.setId(user.getId());
        customUserDetail.setPassword(user.getPassword());
        return customUserDetail ;
    }
~~~~

After that you can retrieve anything from your principal :

    <sec:authentication property="principal.id"/>