如果用户没有登录，那么禁止下载文件

 location ~.*\.(html|htm|gif|jpeg|bmp|jpg|ico|js|css|flv|ttf|woff|eot|svg|shtml|png|doc|exe|docx|swf|wmv|zip|ppt|mpg|mp3|asf|pptx|asx|avi|bmp|dat|db|dot|fla|gsp|hlv|mht|mp2|mpa|mp4|mpv|pptm|psd|ram|rar|rm|rmvb|rtf|shs|tif|wmf|wav|wma|xls|xlsx|pdf)$
        {
                #防止盗链
                default_type application/octet-stream;
                rewrite_by_lua
                        ‘
                         local _, q=string.find(tostring(ngx.var.uri), "dsideal_yy/html/down")

                          if (q ~=  nil) then
                                  ngx.log(ngx.ERR,"#########################"..q);
                                  local cookie_person_id = tostring(ngx.var.cookie_person_id);
                                  if(cookie_person_id == "nil") then
                                        ngx.exit(ngx.HTTP_FORBIDDEN)
                                  end
                           end
                        ‘;


                if ($arg_flag = "download")
                {
                  add_header Cache-Control "private";
                  add_header Accept-Rangles "bytes";

                  add_header Content-Disposition "attachment;filename=$arg_n;filename*=UTF-8‘‘$arg_n;";
                  add_header Pragma  "no-cache";
                  add_header Expires "0";
                }
            root /usr/local/tomcat7/webapps;
            #expires定义用户浏览器缓存的时间为3天，如果静态页面不常更新，可以设置更长，这样可以节省带宽和缓解服务器的压力
            expires      3d;
        }