Moderator: igrr
In my view it is easier / better to use the server.on method.
Look at the examples under ESP8266WebServer e.g HelloServer for a really basic use of server.on or FSBrowser for a more complete way of getting responses from the filing system.
Note that within a server.on request handler one can get any arguments associated with the request very easily using server.arg() rather than having to parse the raw request.