request.getContextPath 上下文,例如 /bignews1 (自带 “ / ”)
request.getScheme() 协议,例如HTTP
request.getServerName() 域名,例如localhost
request.getServerPort() 端口,例如8080
总结:比如,String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + request.getContextPath() ,
结果就是http://localhost:8080/bignews1/