I am trying to pass some parameters from one server to a JSP page on another server, and the receiving JSP page writes those parameters to a text file.
Just use "setRequestProperty" -- "addRequestProperty" does the same thing but won't overwrite an existing value.
You are getting confused by two different uses of the term "request property". In your situation you are setting up an URL Connection which is going to send a request to an arbitrary HTTP server, with new properties you are setting up, in the HTTP headers. The destination server is going to get a new HttpRequest, with properties corresponding to those request property values that you send to it.