1. Unknown initial character set index '255' received from server. Initial client character set can be ...
原因之一：tomcat版本太低
解决之二：mysql版本修改：从'5.1.6'到'5.1.44 '
2. Cannot resolve com.mysq.jdbc.Connection.ping method. Will use 'SELECT 1' instead.
原因之一：driverClassName写错了：把com.mysql.jdbc.Driverv换成 com.mysql.cj.jdbc.Driver
3. Unable to process Jar entry [module-info.class] from Jar
解决之一：把包删掉
4. 转发失败：request.getRequestDispatcher("/login.jsp")，结果网址变成了xxx/LoginServlet
解决之一：不用form提交请求，在form里写个button，给button绑定方法发送请求
解决之二：form的submit事件里方法的返回值写为false
5. javax.net.ssl.SSLException: closing inbound before receiving peer's close_notify
解决之一：在url后加上useSSL=false：url=jdbc:mysql:///bookstore?useSSL=false
