【Mybatis源码探索】 --- 开篇 • 搭建一个最简单的Mybatis框架

源码地址：https://github.com/nieandsun/mybatis-study

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感觉比较简单，有不懂或有兴趣的可以clone下来代码看一下，一看肯定就都懂了。不过多解释了，直接上代码。

1 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.nrsc</groupId>
    <artifactId>mybatis-quick-start</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- 单元测试相关依赖 -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>

        <!-- 日志相关依赖 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.10</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.1.2</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
            <version>1.1.2</version>
        </dependency>

        <!-- mysql驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.17</version>
        </dependency>

        <!-- mybatis相关依赖 -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.3</version>
        </dependency>

        <!--lombok-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.10</version>
        </dependency>
    </dependencies>
</project>

2 主配置文件

• mybatis-config.xml

<?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>

    <properties resource="db.properties"/>

    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>


    <!--配置environment环境 -->
    <environments default="development">
        <!-- 环境配置1，每个SqlSessionFactory对应一个环境 -->
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="UNPOOLED">
                <property name="driver" value="${jdbc_driver}"/>
                <property name="url" value="${jdbc_url}"/>
                <property name="username" value="${jdbc_username}"/>
                <property name="password" value="${jdbc_password}"/>
            </dataSource>
        </environment>

    </environments>

    <!-- 映射文件，指定mapper.xml的位置,有四种方式(详情可以看官网:https://mybatis.org/mybatis-3/configuration.html) -->
    <mappers>
        <mapper resource="mapper/TUserMapper.xml"/>
    </mappers>

</configuration> 

• db.properties

jdbc_driver=com.mysql.cj.jdbc.Driver
jdbc_url=jdbc:mysql://127.0.0.1:3306/mybatis-study?characterEncoding=utf-8&serverTimezone=GMT&useSSL=false
jdbc_username=root
jdbc_password=123456

3 domain、mapper和mapper.xml

• domain类 — TUser

package com.nrsc.mybatis.domain;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

@Getter
@Setter
@ToString
public class TUser {

    private Integer id;

    private String userName;

    private String realName;

    private Byte sex;

    private String mobile;

    private String email;

    private String note;

    private Integer positionId;
}

• mapper类 — TUserMapper

package com.nrsc.mybatis.mapper;

import com.nrsc.mybatis.domain.TUser;

public interface TUserMapper {

    TUser selectByPrimaryKey(Integer id);
}

• mapper.xml — TUserMapper.xml

<mapper namespace="com.nrsc.mybatis.mapper.TUserMapper">

	<select id="selectByPrimaryKey" resultType="com.nrsc.mybatis.domain.TUser"	parameterType="java.lang.Integer">
		select
			id, 
			user_name , 
			real_name , 
			sex, 
			mobile, 
			email, 
			note,
			position_id positionId
		from t_user
		where id = #{id,jdbcType=INTEGER}
	select>
	
mapper>

4 测试启动类

import com.nrsc.mybatis.domain.TUser;
import com.nrsc.mybatis.mapper.TUserMapper;
import lombok.extern.slf4j.Slf4j;
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.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;


@Slf4j
public class MybatisQuickStart {

    private SqlSessionFactory sqlSessionFactory;

    /****
     * 构建全局变量SqlSessionFactory
     * @throws IOException
     */
    @Before
    public void init() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        // 1.读取mybatis配置文件创SqlSessionFactory
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        inputStream.close();
    }


    /***
     * 快速入门1  --- ibatis的方式，其实Mybatis底层也用的这种方式
     */
    @Test
    public void quickStart1() {
        // 2.获取sqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 3.执行查询语句并返回结果 --- 第二次会走缓存
        TUser user = sqlSession.selectOne("com.nrsc.mybatis.mapper.TUserMapper.selectByPrimaryKey", 1);
        TUser user2 = sqlSession.selectOne("com.nrsc.mybatis.mapper.TUserMapper.selectByPrimaryKey", 1);
        // 4.关闭session
        sqlSession.close();
        log.info("user111:" + user);
        log.info("user111:" + user2);
    }

    /***
     * mybatis的方式
     */
    @Test
    public void quickStart2() {
        // 2.获取sqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 3.获取对应mapper
        TUserMapper mapper = sqlSession.getMapper(TUserMapper.class);
        // 4.执行查询语句并返回结果
        TUser user = mapper.selectByPrimaryKey(1);
        //5.关闭session
        sqlSession.close();
        log.info("user222:" + user);
    }
}

5 代码结构

整体的代码结构如下：

6 测试

启动quickStart1或quickStart2测试类，可以打印出如下sql，并获取到一条用户数据，证明Mybatis框架已经搭建成功。