@Override
  public boolean addCustomer(Customer customer) {
    if (null == customer) {
      throw new IllegalArgumentException("customer is null");
    }

    if (customer.getId() == null) customer.setId(customerDao.getNextSequenceNumber());
    return customerDao.insert(customer);
  }
 @Override
 public Integer getNextSequenceNumber() {
   return customerDao.getNextSequenceNumber();
 }