First, it looks like it does not require development of FTP server.
Second, "open the file in a window" is not related to FTP. Even heard of
Separation of concerns?
Finally, all you need is how to use Java to act as an FTP client. But this can be found in million places. Here they are:
http://lmgtfy.com/?q=java+ftp+client[
^].
—SA