一、环境准备

jdk：17

maven：3.9.5

二、下载 MyBatis 源码和 MyBatis-Parent 源码

Mybatis：https://github.com/mybatis/mybatis-3.git

Mybatis-Parent：https://github.com/mybatis/parent.git

建议使用git的方式拉取代码，后期就不需要执行git init

三、创建空项目、导入项目

导入两个项目

注意 mybatis-parent 必须采用 jdk版本：11-23，maven版本： 3.9.5

否则提示：

ERROR] Rule 1: org.apache.maven.enforcer.rules.version.RequireJavaVersion failed with message: [ERROR] Detected JDK version 1.8.0-361 (JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.8.0_361.jdk/Contents/Home/jre) is not in the allowed range [11,12),[17,18),[21,22),[22,23). [ERROR] Rule 2: org.apache.maven.enforcer.rules.version.RequireMavenVersion failed with message: [ERROR] Detected Maven Version: 3.6.3 is not in the allowed range [3.9.5,).

未来可能发生改变

设置为maven 3.9.5

设置为java 17

四、编译 mybatis-parent

执行命令

mvn clean install 

或者通过窗口执行

注意：如果出现Error: One of setGitDir or setWorkTree must be called.

执行命令：git init

五、编译 mybatis

修改成自己特有的版本，方便区分，避免与官网依赖相同版本

执行 maven 命令

mvn install -Dmaven.test.skip=true

PS：建议直接删除test相关文件夹

注意：如果出现：Could not get HEAD Ref, are you sure you have some commits in the dotGitDirectory (currently set to xxx/java-mybatis-source/mybatis-3-master/.git)?

执行命令

git add .
git commit -m 'xxx'

六、测试

1. 添加mybati-test项目
2. 引入依赖

    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.16-DEMO</version>
    </dependency>
    <dependency>
      <groupId>com.mysql</groupId>
      <artifactId>mysql-connector-j</artifactId>
      <version>8.3.0</version>
    </dependency>

3. 添加数据库

create database test;
create table if not exists test.user
(
    id         int auto_increment
        primary key,
    userName   varchar(50) not null,
    createTime datetime    not null
);

4. 添加entity

package com.mcode.entity;

import java.time.LocalDateTime;

/**
 * ClassName: User
 * Package: com.mcode.entity
 * Description:
 *
 * @Author: robin
 * @Version: v1.0
 */
public class User {
    private int id;
    private String userName;

    private LocalDateTime createTime;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public LocalDateTime getCreateTime() {
        return createTime;
    }

    public void setCreateTime(LocalDateTime createTime) {
        this.createTime = createTime;
    }
}

6. 添加 UserMapper

package com.mcode.mapper;

import com.mcode.entity.User;

/**
 * ClassName: UserMapper
 * Package: com.mcode.mapper
 * Description:
 *
 * @Author: robin
 * @Version: v1.0
 */
public interface UserMapper {
   User selectById(int id);
}

7. 添加 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>
    <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/test"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="./mappers/UserMapper.xml"/>
    </mappers>
</configuration>

8. 添加 UserMapper.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.mcode.mapper.UserMapper">
    <!--namespace根据自己需要创建的的mapper的路径和名称填写-->
    <select id="selectById" resultType="com.mcode.entity.User">
        select * from user where id = #{id}
    </select>
</mapper>

9. 测试

package com.mcode;

import com.mcode.entity.User;
import com.mcode.mapper.UserMapper;
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.Reader;

/**
 * Hello world!
 *
 */
public class App 
{
    public static void main( String[] args )
    {
        String resource = "mybatis-config.xml";
        Reader reader;
        try {
            //将XML配置文件构建为Configuration配置类
            reader = Resources.getResourceAsReader(resource);
            // 通过加载配置文件流构建一个SqlSessionFactory  DefaultSqlSessionFactory
            SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);
            // 数据源 执行器  DefaultSqlSession
            SqlSession session = sqlMapper.openSession();
            try {
                UserMapper mapper = session.getMapper(UserMapper.class);
                System.out.println(mapper.getClass());
                User user = mapper.selectById(1);
                System.out.println(user.getUserName());
            } catch (Exception e) {
                e.printStackTrace();
            }finally {
                session.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

问题：Cannot enable lazy loading because Javassist is not available. Add Javassist to your classpath.

看报错信息应该是缺少Javassit的jar包，我们去 mybatis的源码pom.xml把相应的jar复制过来

     <dependency>
      <groupId>ognl</groupId>
      <artifactId>ognl</artifactId>
      <version>3.2.15</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>org.javassist</groupId>
      <artifactId>javassist</artifactId>
      <version>3.27.0-GA</version>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>

总结

不必过于纠结一些错误，对于一些失败的可以考虑直接注释