found the reason why the
Mabitis associated interface operates the database. In the mapper.xml mapping file, I wrote the < insert > < / insert > tag as the < select > < / select > tag, which did not report an error, but did not return the number of rows changed

@Test//
    public void testInsertUser(){
        int row = 0;
        SqlSession sqlSession = sessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        User user = new User(6, "rose", "", 12);
        row = userMapper.insertUser(user);//null
        sqlSession.commit();
        sqlSession.close();
        System.out.println(row);
    };

because it is a query tag, natural data will not be submitted