Server.MapPath cannot find a namespace, workaround

Recently in the public number development, on the Internet to find an example to get the value of the Access_token, need to read the XML file, the result is encountered this problem

Then I introduce the server's namespace

It's obvious that this quote is wrong

the namespace of the online Server.MapPath () : System.Web.HttpContext.Current.Server.MapPath, but I can't find the Add reference.

In the end, I solved it.

Server.MapPath () is the conversion of a relative path to an absolute path

Server.MapPath cannot find a namespace, workaround