Unfortunately, the embedded Jetty seems to be constrained in the ability to create a web context programmatically. Others may be able to share their experience with achieving this.
If you want to create a web context by creating an expanded WAR structure in the JBoss deploy directory, you could move the uploaded files into the appropriate location relative within this directory context. This approach does create problems with portability.
You can also expand the application WAR and place uploaded files within this context which reduces portability problems.
Your other option is covered in more detail in this thread:
http://www.jboss.org/modules/bb/index.html?module=bb&op=viewtopic&t= these are useful starting points.
Thanks a lot,