深度 Mybatis 3 源码分析（一）SqlSessionFactoryBuilder源码分析

MyBatis消除了几乎所有的JDBC代码和参数的手工设置以及对结果集的检索封装。MyBatis可以使用简单的XML或注解用于配置和原始映射，将接口和Java的POJO（Plain Old Java Objects，普通的Java对象）映射成数据库中的记录。

Mybatis环境快速入门

Maven依赖信息

<?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>
<parent>
<artifactId>sourceanalysis</artifactId>
<groupId>com.brian</groupId>
<version>0.0.1-SNAPSHOT</version>
</parent>

<artifactId>mybatis3</artifactId>
<groupId>com.brian</groupId>
<version>0.0.1-SNAPSHOT</version>
<description>源码分析 - mybatis3源码分析</description>

<dependencies>
<!--mysql数据库驱动 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.38</version>
</dependency>

<!-- mybatis ORM框架 -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.1</version>
</dependency>
</dependencies>

</project>

创建mybatis配置文件 mybatis.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>
<!-- 环境配置 -->
<environments default="dev">
<environment id="dev">
<transactionManager type="JDBC"/>
<!-- 数据库连接相关配置 ,这里动态获取config.properties文件中的内容-->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://127.0.0.1:14110/brian?useSSL=false"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
<!-- mapping文件路径配置 -->
<mappers>
<mapper resource="mapper/UserMapper.xml"/>
</mappers>

</configuration>

Mapper配置文件

<?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="mapper.UserMapper">
<select id="getUser" parameterType="int"
resultType="entity.User">
select * from user where id=#{id}
</select>
</mapper>

运行MyBatis代码

import 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;

/**
* @program: architect
* @author: Brian Huang
* @create: 2019-06-04 22
**/
public class MybatisApp {

public static void main(String[] args) {
try {
//1.定义配置文件
String resource = "mybatis.xml";
//2.获取InputStreamReader IO流
Reader reader = Resources.getResourceAsReader(resource);
//3.获取SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
//4.获取Session
SqlSession session = sqlSessionFactory.openSession();
//5.执行mapper接口方法
UserMapper mapper = session.getMapper(UserMapper.class);
System.out.println("--result--: " + mapper.getUser(1).toString());

} catch (IOException e) {
e.printStackTrace();
}
}

}

数据表结构

-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user`  (
`id` int(20) NOT NULL AUTO_INCREMENT,
`username` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '用户名',
`password` varchar(32) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '密码，加密存储',
`phone` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '注册手机号',
`email` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '注册邮箱',
`created` datetime(0) NOT NULL,
`updated` datetime(0) NOT NULL,
PRIMARY KEY (`id`) USING BTREE,
UNIQUE INDEX `username`(`username`) USING BTREE,
UNIQUE INDEX `phone`(`phone`) USING BTREE,
UNIQUE INDEX `email`(`email`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 36 CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '用户表' ROW_FORMAT = Dynamic;

SET FOREIGN_KEY_CHECKS = 1;

Mybatis大体架构流程分析

1. 读取resources获取对应的Reader对象。

Reader reader = Resources.getResourceAsReader(resources);

2. 使用SqlSessionFactoryBuilder获取SqlSessionFactory

SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);

源码分析：

2.1.进入到build 传递reader有参数构造函数

最终执行

2.2. SqlSessionFactoryBuilder使用XMLConfigBuilder解析配置文件，封装成Configuration对象。

注意：parsed = false,避免maybatis.xml被加载多次，因为我们的configuration是全局的所以只能被解析一次

 2.3 执行environmentsElement()  方法

此处for循环是environment可能回配置多个运行环境如dev，test，prod等

 2.4 执行mapperElement()方法 解析mybatis.xml里面的<mappers>节点

这里的Mapper有两种扫描的方式 package和resource，根据我上面的mybatis.xml配置文件，这里会走第一个判断

2.5 执行XMLMapperBuilder的parse()方法，解析UserMapper.xml

2.5.1 isResourceLoaded() 判断避免mapper被重复解析

2.5.2 configurationElement()执行具体的解析UserMapper.xml逻辑

2.5.3 addLoadedResource()方法Mapper路径放入到loadedResoures中

 2.5.4 执行bingMapperForNamesapce() 将UserMapper.XML和UserMapper.java 进行映射

总环下流程图 (PS 图画的不是太好看) 红色框为SqlSessionFactoryBuilder的执行逻辑