MybatisAutoConfiguration.afterPropertiesSet（）
spring初始化
@Override public void afterPropertiesSet() { checkConfigFileExists(); }
N
SqlSessionFactoryBuilder.build(Configuration config)
new DefaultSqlSessionFactory(config)
MybatisAutoConfiguration.sqlSessionFactory()
this.sqlSessionFactory == null
XMLConfigBuilder如果没有工厂类，需要从读取配置文件开始，装载Configration，解析配置文件各个标签等
spring类初始化工厂
InitializingBean.afterPropertiesSet()
buildSqlSessionFactory.afterPropertiesSet()
SqlSessionFactoryBean.getObject()
SpringBoot+Mybatis3.7
buildSqlSessionFactory.buildSqlSessionFactory()
