So you think that the applet should be able to unrestrictedly write files to the SERVER!!!?? That's where
www.host.com is - not on the client's local machine.
Yeah, you can do that - it's called "Code Red"!
Seriously, to write a file to the server, the server has to be willing to accept the file. You can do this fairly simply by opening a URL connection on the client side and aiming it at a servlet on the server that figures out what actual directory to put it in, what actual name to give it, and any other post-prcoessing of the data it wants to do, then does the writing.
A WEB server is <i>not</i> a file server! Considering what's been going on lately, it's just as well. I've had over 1500 attempts by Code Red to break into my webservers since August 1, including a good many from "Code Red II", which WOULD like to write files on my server = without permission!.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.