commit出现错误，怎么办

    public String add() throws Exception {        Transaction tx = null;        Session session = null;        try {            session= countryRegionDAO.getSessionFactory().openSession();            tx=session.beginTransaction();                        CountryRegion region=new CountryRegion();            region.setName(this.name);            session.save(region);                        tx.commit();//-----------执行到这里抛出异常-------            return "success";        }        catch(Exception e)  {            if(tx != null) tx.rollback();            //e.printStackTrace();        } finally {            session.close();        }        return "fail";    }