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_incrementprimary 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 configurationPUBLIC "-//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  DefaultSqlSessionFactorySqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);// 数据源 执行器  DefaultSqlSessionSqlSession 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