Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.

问题原因： 
    升级后的mysql驱动类，Driver位置由com.mysql.jdbc.Driver 变为com.mysql.cj.jdbc.Driver 
解决方案： 
    将数据配置文件里spring.datasource.driver-class-name=com.mysql.jdbc.Driver修改为如下
    spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver