<?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="userMapper">
    <select id="findById" resultType="user" parameterType="int">
        select * from user where id=#{id}
    </select>

    <select id="findAll" resultType="user">
        select * from user
    </select>
</mapper>

public interface UserDao {

    public List<User> findAll() throws IOException;

    public User findById(int id) throws IOException;
}

public class UserDaoImpl implements UserDao {
    public List<User> findAll() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        List<User> userList = sqlSession.selectList("userMapper.findAll");
        return userList;
    }

    public User findById(int id) throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        User user = sqlSession.selectOne("userMapper.findById",id);
        return user;
    }
}

public class ServiceDemo {
    public static void main(String[] args) throws IOException {
        // 创建dao层对象，当前dao层实现是手动编写的
        UserDao userDao = new UserDaoImpl();
        List<User> all = userDao.findAll();
        System.out.println(all);
    }
}

<mapper namespace="com.bearpx.spring.mybatis.dao.UserDao">

    @Test
    public void testProxyDao() throws IOException {
        // 获得核心配置文件
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        // 获得session工厂对象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        // 获得session 会话对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 获得 MyBatis 框架生成的 UserMapper 接口的实现类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        // 执行操作   参数： namespace + id
        User user = userDao.findById(1);
        System.out.println(user);
        // 释放资源
        sqlSession.close();
    }

public class ServiceDemo {
    public static void main(String[] args) throws IOException {
        // 获得核心配置文件
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        // 获得session工厂对象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        // 获得session 会话对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        // 执行操作   参数： namespace+id
        User user = userDao.findById(1);
        System.out.println(user);
        // 释放资源
        sqlSession.close();
    }
}