dao层实现数据库连接链接分享
https://zhengqing.blog.csdn.net/article/details/82842426?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-7.control&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-7.control
上图为类包分布