MyBatis的Dao实现层有两种方式
一、传统开发⽅式
1、编写IUserDao接⼝
package study.lagou.com.dao;
import study.lagou.com.pojo.User;
import java.io.IOException;
import java.util.List;
public interface IUserDao {
List<User> findAll() throws IOException;
}
2、编写UserDaoImpl实现
package study.lagou.com.dao.impl;
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 study.lagou.com.dao.IUserDao;
import study.lagou.com.pojo.User;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
/**
* @Description: 功能描述
* @Author houjh
* @Email: happyxiaohou@gmail.com
* @Date: 2021-3-23 15:19
*/
public class UserDaoImpl implements IUserDao {
@Override
public List<User> findAll() throws IOException {
//1、Resources工具类，完成配置文件的加载，将配置文件加载成字节输入流
InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
//2、SqlSessionFactoryBuilder通过构建者模式解析配置文件，并创建了sqlSessionFactory工厂
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
//3、sqlSessionFactory通过工厂模式来创建sqlSession,此处需要注意sqlSessionFactory.openSession()会默认开启一个事务，但是
//该事务不会自动提交，在进行增删改操作时，需要手动提交事务，也要直接通过sqlSessionFactory.openSession(true)方法来设置自动提
//交事务信息
SqlSession sqlSession = sqlSessionFactory.openSession();
//4、sqlSession调用方法，查询所有调用selectList 查询单个调用selectOne 添加调用insert 修改调用update 删除调用delete
List<User> users = sqlSession.selectList("study.lagou.com.mapper.findAll");
//方法调用完成注意关闭sqlSession
sqlSession.close();
return users;
}
}
3、编写测试类进行传统方法测试
package study.lagou.com.test;
import org.junit.Test;
import study.lagou.com.dao.IUserDao;
import study.lagou.com.dao.impl.UserDaoImpl;
import study.lagou.com.pojo.User;
import java.io.IOException;
import java.util.List;
/**
* @Description: MyBatis传统开发方式测试
* @Author houjh
* @Email: happyxiaohou@gmail.com
* @Date: 2021-3-22 19:48
*/
public class MyBatisTraditionalTest {
@Test
public void testFindAll() throws IOException {
IUserDao userDao = new UserDaoImpl();
List<User> users = userDao.findAll();
for (User user : users) {
System.out.println(user);
}
}
}
二、代理开发⽅式
代理开发⽅式介绍
采⽤ Mybatis 的代理开发⽅式实现 DAO 层的开发，这种⽅式是我们后⾯进⼊企业的主流。
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：
1、 Mapper.xml⽂件中的namespace与mapper接⼝的全限定名相同
2、Mapper接⼝⽅法名和Mapper.xml中定义的每个statement的id相同
3、 Mapper接⼝⽅法的参数类型和mapper.xml中定义的每个sql的parameterType的类型相同
4、Mapper接⼝⽅法的返回值类型和mapper.xml中定义的每个sql的resultType的类型相同
为不影响之前代码的演示使用，我们不对之前的代码进行修改，直接新建一套接口及mapper.xml配置文件
1、编写IUserProxyDao接⼝
package study.lagou.com.dao;
import study.lagou.com.pojo.User;
import java.util.List;
public interface IUserProxyDao {
List<User> findAll();
}
2、编写UserProxyMapper.xml配置文件
<?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="study.lagou.com.dao.IUserProxyDao">
<!--查询方法-->
<select id="findAll" resultType="study.lagou.com.pojo.User">
SELECT * FROM user
</select>
</mapper>
3、修改sqlMapConfig.xml核心配置文件，在Mappers中将引入UserProxyMapper.xml配置文件
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&serverTimezone=Hongkong&characterEncoding=utf-8&autoReconnect=true"/>
<property name="username" value="root"/>
<property name="password" value="111111"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="study/lagou/com/mapper/UserMapper.xml"/>
<mapper resource="study/lagou/com/mapper/UserProxyMapper.xml"/>
</mappers>
</configuration>
4、编写测试类
package study.lagou.com.test;
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 org.junit.Test;
import study.lagou.com.dao.IUserProxyDao;
import study.lagou.com.pojo.User;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
/**
* @Description: MyBatis传统开发方式测试
* @Author houjh
* @Email: happyxiaohou@gmail.com
* @Date: 2021-3-22 19:48
*/
public class MyBatisProxyTest {
@Test
public void testFindAll() throws IOException {
InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
IUserProxyDao mapper = sqlSession.getMapper(IUserProxyDao.class);
List<User> all = mapper.findAll();
for (User user : all) {
System.out.println(user);
}
}
}
上一篇笔记地址:https://www.jianshu.com/p/f138ca176525
