MyBatis源码解析（一）：从一个简单的MyBatis查询开始

妖狐艹你老母 2022-02-26 13:28 155阅读 0赞

一，简单的MyBatis用例

1，Maven依赖引入

<dependencies>
        <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>4.11</version>
          <scope>test</scope>
        </dependency>
        <dependency>
          <groupId>org.mybatis</groupId>
          <artifactId>mybatis</artifactId>
          <version>3.4.2</version>
        </dependency>
        <dependency>
          <groupId>log4j</groupId>
          <artifactId>log4j</artifactId>
          <version>1.2.17</version>
        </dependency>
        <dependency>
          <groupId>mysql</groupId>
          <artifactId>mysql-connector-java</artifactId>
          <version>5.1.6</version>
        </dependency>
        <dependency>
          <groupId>org.projectlombok</groupId>
          <artifactId>lombok</artifactId>
          <version>1.16.22</version>
        </dependency>
      </dependencies>

2，MyBatis核心配置文件 -- mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
    <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
    
    <configuration>
    
        <properties resource="jdbc.properties" />
        
        <settings>
            <setting name="logImpl" value="LOG4J"/>
        </settings>
    
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC" />
                <dataSource type="POOLED">
                    <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>
        <mappers>
            <mapper resource="mapper/UserMapper.xml" />
        </mappers>
    
    </configuration>

3，Mapper.java

package com.gupao.mapper;
    
    import com.gupao.domain.UserVO;
    import org.apache.ibatis.annotations.Param;
    
    /**
     * @author pj_zhang
     * @create 2019-03-25 22:35
     **/
    public interface UserMapper {
    
        UserVO selectUserById(@Param("id") Integer id);
    
    }

4，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="com.gupao.mapper.UserMapper">
    
        <select id="selectUserById" resultType="com.gupao.domain.UserVO">
          SELECT
            ID AS id,
            USERNAME AS username,
            PASSWORD AS password,
            AGE AS age
          FROM
            USER_T
          WHERE
            ID = #{id, jdbcType=NUMERIC}
        </select>
    
    </mapper>

5，MyBatis直连代码

package com.gupao.test;
    
    import com.gupao.domain.UserVO;
    import com.gupao.mapper.UserMapper;
    import lombok.extern.log4j.Log4j;
    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;
    
    /**
     * @author pj_zhang
     * @create 2019-03-25 22:39
     **/
    @Log4j
    public class MyBatisTest {
    
        public static void main(String[] args) throws IOException {
            // mybatis基础配置文件路径及文件名
            String resource = "mybatis-config.xml";
            // 获取配置文件输入流
            InputStream inputStream = Resources.getResourceAsStream(resource);
            // 通过文件输入流进行XML文件解析, 添加配置信息到Configuration
            // Configuration.addMapper()通过调用
            // 直接返回DefaultSqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            // openSession, 获取DefaultSqlSession
            // 在内部生成Executor, 并同Configuration一同注入到DefaultSqlSession中
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                // 根据Mapper名称从SqlSession中获取Mapper代理对象
                // 内部通过Configuration.mapperRegistry.knownMappers调用链获取Mapper对象
                // 并通过动态代理获取该Mapper对象的代理对象, MapperProxy
                UserMapper mapper = sqlSession.getMapper(UserMapper.class);
                // 通过动态代理invoke()调用
                // 底层通过Executor.query()执行SQL语句获取结果
                // ORM映射通过ResultSetHandler完成
                UserVO userVO = mapper.selectUserById(1);
                System.out.println(userVO);
            } catch (Exception e) {
               log.info(e);
            }
        }
    
    }

6，各阶段相关注释在代码中已经注释完成，源码分段解析会根据执行顺序分模块进行大概解析

7，源码解析只会了解MyBatis底层实现原理和流程，说明问题即可，不追求每一个方法都进行详细分析

二，MyBatis源码分段解析

\* 初始化配置文件，并获取SqlSessionFactory

链接：[https://blog.csdn.net/u011976388/article/details/88903330][https_blog.csdn.net_u011976388_article_details_88903330]

\* 通过SqlSessionFactory获取SqlSession

链接：[https://blog.csdn.net/u011976388/article/details/88904251][https_blog.csdn.net_u011976388_article_details_88904251]

\* 通过SqlSession获取Dao层接口的执行Mapper

链接：[https://blog.csdn.net/u011976388/article/details/88907538][https_blog.csdn.net_u011976388_article_details_88907538]

\* 通过Mapper执行Statement

链接：[https://blog.csdn.net/u011976388/article/details/88919193][https_blog.csdn.net_u011976388_article_details_88919193]

\* 通过ResultSetHandler实现ORM映射

链接：[https://blog.csdn.net/u011976388/article/details/88922016][https_blog.csdn.net_u011976388_article_details_88922016]

\* 手写简易MyBatis

链接：[https://blog.csdn.net/u011976388/article/details/88927897][https_blog.csdn.net_u011976388_article_details_88927897]

[https_blog.csdn.net_u011976388_article_details_88903330]: https://blog.csdn.net/u011976388/article/details/88903330
[https_blog.csdn.net_u011976388_article_details_88904251]: https://blog.csdn.net/u011976388/article/details/88904251
[https_blog.csdn.net_u011976388_article_details_88907538]: https://blog.csdn.net/u011976388/article/details/88907538
[https_blog.csdn.net_u011976388_article_details_88919193]: https://blog.csdn.net/u011976388/article/details/88919193
[https_blog.csdn.net_u011976388_article_details_88922016]: https://blog.csdn.net/u011976388/article/details/88922016
[https_blog.csdn.net_u011976388_article_details_88927897]: https://blog.csdn.net/u011976388/article/details/88927897