报错信息：
WARN: 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. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
查看翻译显示是数据库连接出的问题
解决方案：设置useSSL=false
String url = "jdbc:mysql://127.0.0.1/leaning?useSSL=false";//在最后加上?useSSL=false这样就解决了。
来源地址：https://blog.csdn.net/weixin_45134559/article/details/129377319
