public void insertStudet() throws Exception {
    SqlSession sqlSession = null;
    try{
        sqlSession=MybatisUtils.openSession();
        Student student = new Student();
        student.setRegNo(20171208);
        student.setName("言豫津");
        student.setSex("男");
        student.setMajor("哲学系");
        student.setGrade("2017");
        student.setAge(26);
        sqlSession.insert("student.insertStudent",student);
    }catch(Exception e){
        throw e;
    }finally{
        MybatisUtils.releaseSession(sqlSession);
    }
}

上面代码中没有调用sqlSession.commit();对事务提交，jUnit执行完成后注意到数据库中没有插入新的数据，修改代码如下后再次执行，观察到数据库添加了数据但是自增id跳过了一位数字，我怀疑是之前没有提交的事务造成的，我的推测正确吗？像前面代码这样没有手动提交的事务Mybatis会定期自动提交吗？rollback()回滚事务会造成主键自增值的改变吗？

public void insertStudet() throws Exception {
    SqlSession sqlSession = null;
    try{
        sqlSession=MybatisUtils.openSession();
        Student student = new Student();
        student.setRegNo(20171208);
        student.setName("言豫津");
        student.setSex("男");
        student.setMajor("哲学系");
        student.setGrade("2017");
        student.setAge(26);
        sqlSession.insert("student.insertStudent",student);
        sqlSession.commit();
    }catch(Exception e){
        if(sqlSession!=null){
            sqlSession.rollback();
        }
        throw e;
    }finally{
        MybatisUtils.releaseSession(sqlSession);
    }
}

<insert id="insertGoods" parameterType="com.imooc.mybatis.entity.Goods">
    INSERT t_goods VALUE(NULL,#{title},#{subTitle},#{originalCost},#{currentPrice},#{discount},#{isFreeDelivery},#{categoryId});
    <selectKey resultType="Integer" keyProperty="goodsId">
        SELECT last_insert_id();
    </selectKey>
</insert>

​