简单的用户增删改查，增删改查的返回值均为boolean型，页面仅有error.jsp、index.jsp、success.jsp、add.jsp、delete.jsp、update.jsp和select.jsp仅供参考-Simple user CRUD, CRUD return values are boolean type, the page just error.jsp, index.jsp, success.jsp, add.jsp, delete.jsp, update.jsp and