传统方式实现
1. 编写UserDao接口
public interface UserDao {
List<User> findAll() throws IOException;
}2. 编写映射文件
<?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="findAll" resultType="user">
select * from user
</select>
</mapper>3. 编写UserDaoImpl实现
public class UserDaoImpl implements UserDao {
@Override
public List<User> findAll() throws IOException {
//加载核心配置文件
InputStream inputStream = Resources.getResourceAsStream("sqlMapConfig.xml");
//获得sqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//获得sqlSession对象
SqlSession session = sqlSessionFactory.openSession();
//执行sql语句
List<User> userList = session.selectList("userMapper.findAll");
session.close();
return userList;
}
}使用代理的dao层实现
Mapper 接口开发方法只需要程序员编写Mapper 接口（相当于Dao 接口），由Mybatis框架根据接口定义创建接口的动态代理对象，代理对象的方法体同上边Dao接口实现类方法。
Mapper 接口开发需要遵循以下规范：
- Mapper.xml文件中的namespace与mapper接口的全限定名相同
- Mapper接口方法名和Mapper.xml中定义的每个statement的id相同
- Mapper接口方法的输入参数类型和mapper.xml中定义的每个sql的parameterType的类型相同
- Mapper接口方法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同
==一一对应==
测试
@Test
public void proxyTest() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
//获得MyBatis框架生成的UserMapper接口的实现类
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> userList = mapper.findAll();
System.out.println(userList);
}