MyBatis是支援普通 SQL查詢，儲存過程和高階對映的優秀持久層框架，具有的特點，避免了JDBC對資料庫進行頻繁連線開啟和關閉造成資料庫資源浪費和硬編碼現象的出現。

MyBatis開發dao具有兩種開發方式，原始的dao開發和mapper代理的開發方式
Dao開發方式需要dao介面和dao實現類，向dao實現類中注入SqlSessionFactory，在方法體內通過SqlSessionFactory建立SqlSession

public interface UserDao {	
	
	public User findUserById(int id) throws Exception;
}

public class UserDaoImpl implements UserDao {

	
	private SqlSessionFactory sqlSessionFactory;
	public UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
		this.sqlSessionFactory = sqlSessionFactory;
	}
	@Override
	public User findUserById(int id) throws Exception {
		SqlSession sqlSession = sqlSessionFactory.openSession();
		User user = sqlSession.selectOne("User.findUserById", id);
		sqlSession.close();
		return user;
	}
}
 

<?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="User ">
       <select id="findUserById" parameterType="int" resultType="cn.itcast.mybatis.po.User">
		SELECT * FROM USER WHERE id=#{value}
	</select>
</mapper>
 

public class UserDaoImplTest {
	private SqlSessionFactory sqlSessionFactory;
	@Before
	public void setUp() throws Exception {	
		String resource = "SqlMapConfig.xml";		
		InputStream inputStream = Resources.getResourceAsStream(resource);		
		sqlSessionFactory = new SqlSessionFactoryBuilder()
				.build(inputStream);
	}
	@Test
	public void testFindUserById() throws Exception {
		UserDao userDao = new UserDaoImpl(sqlSessionFactory);
		User user = userDao.findUserById(1);
	}
}
 

Dao開發方式的侷限性主要在於dao介面實現類方法中存在冗餘並且存在硬編碼。

mapper代理的開發方式需要mapper.xml對映檔案

<mapper namespace="cn.itcast.mybatis.mapper.UserMapper">
<select id="findUserList" parameterType="cn.itcast.mybatis.po.UserQueryVo" 
			resultType="cn.itcast.mybatis.po.UserCustom">
	SELECT * FROM USER WHERE id=#{value}
	</select>
<mappers>

public User findUserById(int id) throws Exception;	

<mappers>
     <mapper resource="sqlmap/User.xml"/>
</mappers>

@Test
	public void testFindUserById () throws Exception {	
		SqlSession sqlSession = sqlSessionFactory.openSession();		
		UserMapper userMapper = sqlSession.getMapper(UserMapper.class);		
		List<User> list = userMapper.findUserById ("1");	
		sqlSession.close();