PrintWriter writer = resp.getWriter();//响应流
String contextPath = req.getContextPath();//返回站点根目录
resp.sendRedirect(contextPath);//重定向
Enumeration<String> paraNames = req.getParameterNames();/*提取前端页面请求的所有参数*/
session.invalidate();//销毁session标签：JavaWeb,contextPath,11.22,用到,req,session,resp From： https://www.cnblogs.com/creeperrr/p/16914031.html