1.报错：The server time zone value '???ú±ê×??±??' is unrecognized or represents
解决方法：在jdbc连接的url后面加上serverTimezone=GMT即可
private String dbUrl = "jdbc:mysql://localhost:3306/user?useSSL=false&serverTimezone=GMT";
2. 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.
解决方法：1.在数据库连接的url中添加useSSL=false;2.url中添加useSSL=true，并且提供服务器的验证证书
jdbc:mysql://localhost:3306/user?useSSL=false
3.报错：java.sql.SQLException: Unknown system variable 'query_cache_size'
驱动器版本过低，无法连接。
解决方法：下载对应的驱动器版本。
mysql-connector-java驱动器各版本下载链接：http://mvnrepository.com/artifact/mysql/mysql-connector-java