java.sql.SQLException: Unknown initial character set index '255' received from server. Initial client character set can be forced via the 'characterEncoding' property.解决方案

解决方案：

1. 首先查看数据库的版本号，删除旧的jar包，将mysql-connector-java.jar更换成对应版本号
   
2. 同时在连接数据库的url后加上?useUnicode=true&characterEncoding=utf-8