如何重用/扩展封闭的java webapp（.ear）？

I've got webapp project written in java (.ear). It is running under glassfish-3 server. I really have to extend its functonality. but there is no way to change even a line of it. Is it possible to wrap that webapp or anything else (it has no API, only html for user)? I know it's very generic, but i cannot provide a code or other useful things.I've got webapp project written in java (.ear).