传统方式就是在项目下边建立dao包，里面包含接口及其实现类，文件结构如下： UserMapper.java
package com.example.demo.dao;import com.example.demo.domain.User;import java.io.IOException;import java.util.List;public interface UserMapper {List<User> findAll() throws IOException;}UserMapperImpl.java
package com.example.demo.dao.impl;import com.example.demo.dao.UserMapper;import com.example.demo.domain.User;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;import java.util.List;public class UserMapperImpl implements UserMapper {@Overridepublic List<User> findAll() throws IOException {InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();List<User> userList = sqlSession.selectList("userMapper.findAll");sqlSession.close();return userList;}}测试其实现：
package com.example.demo.service;import com.example.demo.dao.UserMapper;import com.example.demo.domain.User;import java.io.IOException;import java.util.List;public class ServiceDemo {public static void main(String[] args) throws IOException {// 创建dao层对象，目前dao层是手动编写的UserMapper userMapper = new UserMapperImpl();List<User> all = userMapper.findAll();System.out.println(all);}}其实这里边就是用MyBatis提供的API调用MyBatis配置，这个内容在刚开始学MyBatis的时候有提到过：【Spring集成MyBatis】MyBatis诞生及代码快速入门（非注解开发）
2. MyBatis的代理开发方式——仅需写接口在上面的代码中，其实很多代码都是重复的，比如获取sqlSession的代码：
InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();而sql语句的代码又是半重复的，只有括号里面的内容会发生变化：
List<User> userList = sqlSession.selectList("userMapper.findAll");在这里介绍MyBatis的代理开发方式，其需要遵循一定的规范 即如下的对应部分应该相同： 使用以上介绍的开发方式，我们就不需要再写接口的实现类了，只需要让接口与XML文件中的定义对应即可。 此时，我的XML文件和接口分别为： UserMapper.xml
<?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.demo.dao.UserMapper"><select id="findAll" resultType="user">select * from user</select></mapper>UserMapper.java
package com.example.demo.dao;import com.example.demo.domain.User;import java.io.IOException;import java.util.List;public interface UserMapper {List<User> findAll() throws IOException;}测试的时候，只需要通过sqlSession.getMapper()来获得对应类的实现配置即可
package com.example.demo.service;import com.example.demo.dao.UserMapper;import com.example.demo.domain.User;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;import java.util.List;public class ServiceDemo {public static void main(String[] args) throws IOException {InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);SqlSession sqlSession = sqlSessionFactory.openSession();UserMapper userMapper = sqlSession.getMapper(UserMapper.class);List<User> userList = userMapper.findAll();System.out.println(userList);}} 假如带参数查询，操作也是类似的，在XML文件中加上： <select id="findById" parameterType="int" resultType="user">select * from user where id=#{id}</select>接口中加上：
User findById(int id);实现时调用：
User user = userMapper.findById(1);即可获得对应的user结果
