Mybatis报Type interface *.*Mapper is not known to the MapperRegis_开发_开发者

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", www.devze.com"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 SqlSession
        sqlSession.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Map编程per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

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

方法二：使用其他方法是否正确

换一种方法试试，SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。示例代码如下：

public class Test {
    public编程 static void main(String[] args) throws IOException {
        DataSource dataSource = new PooledDataSource("com.mysql.jdbc.Driver", "jdbc:mysql://localhost:3306/spring_data?charphpacterEncoding=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 SqlSession
        sqlSession.close();
    }
}

运行成功，如图所示

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

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 JdphpbcTransactionFactory();
        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 SqlSession
        sqlSession.close();
    }
}

问题解决。

最开始看官网给的代码片段，以为可以去掉addMapper的步骤，后来才想起不注册的话怎么获取呢？啧~还是太粗心了呀！！！

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