mybatis中Mapper接口如何实例化的(为什么mybatis的mapper没有实现类)

public class UserMapperTest {
   
   
	@Test
	public void testQueryUserById() throws IOException {
   
   
		String resource ="mybatis/mybatis-config.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
		SqlSession sqlSession = sqlSessionFactory.openSession(true);
		UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
		User user = userMapper.queryUserById(1l);
		System.out.println(user);
	}
}

接上篇mybatis内部运行原理
跟踪sqlSession.getMapper(UserMapper.class)方法:;来到接口SqlSession的实现类SqlSessionTemplate

 public <T> T getMapper(Class<T> type) {
   
   
    return getConfiguration().getMapper(type, this);
  }

定位到configuration.getMapper(type, this),来到类Configuration

public <T>