前言
工作这么多年，ORM框架一直选择Mybatis框架。 Mybatis的使用方式也一直在变，总体来说是越来越简单。写篇文章对各使用方式做个总结...
正文
一、Mybatis典型用法
1. 正常执行流程
♦ 配置文件 - 全局配置信息和映射文件信息。全局配置信息包括：数据库配置和事务配置。映射文件就是SQL相关的
♦ Mybatis读取配置文件生成SqlSessionFactory，即回话工厂
♦ 获取SqlSession, 做CRUD操作。但真正做这个事情的是底层的executor。
♦ Executor执行器把SQL分装到MappedStatement对象中。该对象包括：SQL, 输入参数映射信息和输出结果映射信息。
2. 案例
2.1 建表
CREATE TABLE `user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `username` varchar(20) , `password` varchar(20) , `age` int(11) , PRIMARY KEY (`id`) )
2.2 全局配置文件
<?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.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3307/book"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mybatis/User.xml"/>
</mappers>
</configuration>
2.3 mapper.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="user">
<select id="findUserById" parameterType="int" resultType="com.mybatis.User">
select * from user where id = #{id}
</select>
<select id="findUserAll" resultType="com.mybatis.User">
select * from user
</select>
<insert id="insertUser" parameterType="com.mybatis.User">
insert into user(username,password,age) values(#{username},#{password},#{age})
</insert>
<delete id="deleteUserById" parameterType="int">
delete from user where id=#{id}
</delete>
<update id="updateUserPassword" parameterType="com.mybatis.User">
update user set password=#{password} where id=#{id}
</update>
</mapper>
2.4 Dao 接口
package com.mybatis.dao;
import com.mybatis.User;
import java.util.List;
public interface UserDao {
public User findUserById(int id) throws Exception ;
public List<User> findAllUsers() throws Exception;
public void insertUser(User user) throws Exception;
public void deleteUserById(int id) throws Exception;
public void updateUserPassword(User user) throws Exception;
}
2.5 DaoImpl
package com.mybatis.dao.impl;
import com.mybatis.User;
import com.mybatis.dao.UserDao;
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 UserDaoImpl implements UserDao {
private static SqlSessionFactory factory = null;
static {
String resource = "mybatis/SqlMapConfig.xml";
InputStream inputStream = null;
try {
inputStream = Resources.getResourceAsStream(resource);
} catch (IOException e) {
e.printStackTrace();
}
factory = new SqlSessionFactoryBuilder().build(inputStream);
}
public static SqlSession getSession(){
return factory.openSession();
}
@Override
public User findUserById(final int id) throws Exception {
return getSession().selectOne("user.findUserById",id);
}
@Override
public List<User> findAllUsers() throws Exception {
return null;
}
@Override
public void insertUser(final User user) throws Exception {
}
@Override
public void deleteUserById(final int id) throws Exception {
}
@Override
public void updateUserPassword(final User user) throws Exception {
}
}
2.6 User类
package com.mybatis;
import lombok.Data;
@Data
public class User {
private Integer id;
private String username;
private String password;
private Integer age;
}
2.7 测试类
package com.mybatis.dao;
import com.mybatis.User;
import com.mybatis.dao.impl.UserDaoImpl;
import org.junit.Test;
public class UserDaoTest {
@Test
public void testFindUserById() throws Exception{
UserDao userDao = new UserDaoImpl();
User user = userDao.findUserById(7);
System.out.println(user);
}
}
二、Mapper代理开发方式
Mapper代理的开发方式，我们只需要编写mapper接口，不需要再Dao类，MyBatis会为我们生成代理类。代理开发方式应当遵循以下条件：
♦ mapper接口的全限定名要和mapper映射文件的namespace的值相同。
♦ mapper接口的方法名称要和mapper映射文件中的statement的id相同。
♦ mapper接口的方法参数只能有一个，且类型要和mapper映射文件中statement的parameterType的值保持一致。
♦ mapper接口的返回值类型要和mapper映射文件中statement的resultType值或resultMap中的type值保持一致。
案例:
1. 建表 同2.1
2. 全局配置 同2.2
3. mapper.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">
<!--参考四要素-->
<mapper namespace="com.mybatis2.dao.UserDao">
<select id="findUserById" parameterType="int" resultType="com.mybatis2.User">
select * from user where id = #{id}
</select>
<select id="findUserAll" resultType="com.mybatis2.User">
select * from user
</select>
<insert id="insertUser" parameterType="com.mybatis.User">
insert into user(username,password,age) values(#{username},#{password},#{age})
</insert>
<delete id="deleteUserById" parameterType="int">
delete from user where id=#{id}
</delete>
<update id="updateUserPassword" parameterType="com.mybatis.User">
update user set password=#{password} where id=#{id}
</update>
</mapper>
4.mapper类：类名无所谓，用*Dao或者*Mapper都可以
package com.mybatis2.dao;
import com.mybatis2.User;
import java.util.List;
public interface UserDao {
public User findUserById(int id) throws Exception ;
public List<User> findUserAll() throws Exception;
public void insertUser(User user) throws Exception;
public void deleteUserById(int id) throws Exception;
public void updateUserPassword(User user) throws Exception;
}
5. User类同2.5
6. 测试类
package com.mybatis.dao;
import com.mybatis2.dao.UserDao;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.BeforeClass;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
public class UserDaoTest2 {
private static SqlSessionFactory factory = null;
@BeforeClass
public static void init(){
String resource = "mybatis/SqlMapConfig.xml";
InputStream inputStream = null;
try {
inputStream = Resources.getResourceAsStream(resource);
} catch (IOException e) {
e.printStackTrace();
}
factory = new SqlSessionFactoryBuilder().build(inputStream);
}
@Test
public void testFindUserById() throws Exception{
UserDao mapp = factory.openSession().getMapper(UserDao.class);
System.out.println(mapp.findUserById(7));
}
}
三、与Spring框架的集成
相关背景，使用方式官方文档已经很详细了。参考官方文档 - http://www.mybatis.org/spring/