Java连接数据库时可以照常运行，但是会出现以下警告：
Fri Sep 07 23:54:02 CST 2018 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.
出现该原因是，虽然已经建立了SSL的连接，但是没有进行身份验证，所以会出现警告，但是不是报错。
解决方案如下：
在连接数据库的URL中加上：?useUnicode=true&characterEncoding=utf-8&useSSL=false该语句即可。
完整的语句：
Connection con = (Connection)DriverManager.getConnection
("jdbc:mysql://localhost:3306/testjdbcuseUnicode=true&characterEncoding=utf-8&useSSL=false", "root", "123456");