how to read write a remote file using applet

If the file is available on a web server on the same host as the applet, then you can just use java.net.URL to open an HTTP connection (you use url.connect() and get a HttpURLConnection). Pretty easy.

Then open a URL and POST to it. (Or PUT if the server is so configured.)You'll need some server-side functionality to know how to deal with a POST or PUT -- but that would be the case if you were opening raw sockets, as well.