Look up user in Spring

CommonController.java

protected String getUser() {

        String username;

        LOGGER.debug("getAuthentication().getName():"
                + SecurityContextHolder.getContext().getAuthentication()
                .getName());

        Object obj = SecurityContextHolder.getContext().getAuthentication()
                .getPrincipal();

        if (obj instanceof UserDetails) {
            username = ((UserDetails) obj).getUsername();
        } else {
            username = obj.toString();
        }
        LOGGER.debug("getUser:" + username);

        return username;
    }