@Override
 public User create(User user) {
   return userDao.create(user);
 }
 @Override
 public void delete(String id) {
   userDao.delete(id);
 }
 @Override
 public User get(String userId) {
   return userDao.get(userId);
 }
 @Override
 public void update(String userId, User user) {
   userDao.update(userId, user);
 }
 @Override
 public Collection<User> list() {
   return userDao.list();
 }