解决Mybatis报Type interface *.*Mapper is not known to the MapperRegis

解决Mybatis报Type interface .Mapper is not known to the MapperRegis

问题发现
问题解决
- 方法一：检查Mapper文件的namespace路径是否正确
- 方法二：使用其他方法是否正确

问题发现

在学习MyBatis框架的时候，不使用 XML 构建 SqlSessionFactory，调用Mapper的接口，报类型接口没有注册。

示例代码如下：

public class Test {public static void main(String[] args) throws IOException {DataSource dataSource = new PooledDataSource("com.mysql.jdbc.Driver", "jdbc:mysql://localhost:3306/spring_data?characterEncoding=utf-8&useSSL=false", "root", "123456");TransactionFactory transactionFactory = new JdbcTransactionFactory();Environment environment = new Environment("development", transactionFactory, dataSource);org.apache.ibatis.session.Configuration configuration = new org.apache.ibatis.session.Configuration(environment);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);SqlSession sqlSession = sqlSessionFactory.openSession();UserMapper userMapper = sqlSession.getMapper(UserMapper.class);List<User> users = userMapper.selectByUser();// 关闭 SqlSessionsqlSession.close();}
}
public interface UserMapper {List<User> selectByUser();
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mybatisstudy.dao.UserMapper"><select id="selectByUser" resultType="com.example.mybatisstudy.User">select * from user;</select>
</mapper>

网上说都是命名空间的错误，发现命名空间也没问题。然后进行一系列的问题排查。

问题解决

方法一：检查Mapper文件的namespace路径是否正确

这也是网上解决方法最多的一种，貌似大部分人都是遇到这种错误。

先确认映射的类名是否正确。
在确认包路径使用的.点（com.*.*.Object）而不是/左斜杠（com/*/*/Object）或\右斜杠（com\*\*\Object），如果错误请修改为.点。
如果鼠标悬浮到路径上，显示下划线说明配置正确。

如图所示
在这里插入图片描述

方法二：使用其他方法是否正确

后面切换到，使用XML 中构建 SqlSessionFactory方法，示例代码如下：

public class Test {public static void main(String[] args) throws IOException {DataSource dataSource = new PooledDataSource("com.mysql.jdbc.Driver", "jdbc:mysql://localhost:3306/spring_data?characterEncoding=utf-8&useSSL=false", "root", "123456");TransactionFactory transactionFactory = new JdbcTransactionFactory();Environment environment = new Environment("development", transactionFactory, dataSource);org.apache.ibatis.session.Configuration configuration = new org.apache.ibatis.session.Configuration(environment);configuration.addMapper(UserMapper.class);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);SqlSession sqlSession = sqlSessionFactory.openSession();List<User> selectByUser = sqlSession.selectList("selectByUser");// 关闭 SqlSessionsqlSession.close();}
}

运行成功，如图所示

在这里插入图片描述
然后逐个代码排除，根据错误提示（未注册）发现少了configuration.addMapper()方法的代码，加上后，运行成功。

示例代码如下

public class Test {public static void main(String[] args) throws IOException {DataSource dataSource = new PooledDataSource("com.mysql.jdbc.Driver", "jdbc:mysql://localhost:3306/spring_data?characterEncoding=utf-8&useSSL=false", "root", "123456");TransactionFactory transactionFactory = new JdbcTransactionFactory();Environment environment = new Environment("development", transactionFactory, dataSource);org.apache.ibatis.session.Configuration configuration = new org.apache.ibatis.session.Configuration(environment);configuration.addMapper(UserMapper.class);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);SqlSession sqlSession = sqlSessionFactory.openSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> users = mapper.selectByUser();// 关闭 SqlSessionsqlSession.close();}
}