@Override
    public int add(Student stu) throws IOException {
        String config="MyBatis_config.xml";
         Reader reader=Resources.getResourceAsReader(config);
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader);
        //openSession底层发生了什么
        SqlSession session = factory.openSession();
        
        //insert底层发生了什么
        int result = session.insert("insertStudent",stu);
        //为什么session可以提交事务
        session.commit();
        //为什么session.close()不会回滚事务
        session.close();
        return result;
    }