最近用idea写了一个程序，中间把mysql从5.7升级到了8.0.原来程序正常，升级之后报错！

idea程序连接MySQL数据库失败Communications link failure
报错The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.

首先检查一下url连接串是不是有错误，我这里之前程序可以正常运行肯定没问题。后来查阅资料说是需要吧com.mysql.jdbc.Driver换成com.mysql.cj.jdbc.Driver。改了之后问题依旧存在！直接命令访问还是用工具连接都正常可以连通，用程序跑就报错！后来偶然间发现程序连接时会报如下警告：

        Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set.
 

猜测可能是数据库升级之后会校验SSL，在数据库连接的url中添加ueSSL=false跳过证书验证，问题解决！记录一下！

spring:
  datasource:
    username: 用户
    password: 密码
    url: jdbc:mysql://127.0.0.1:3306/xx?useUnicode=true&characterEncoding=utf8&useSSL=false
    driver-class-name: com.mysql.cj.jdbc.Driver