The servlets destroy method is called as the servlet is about to be unloaded. You could cancel the timer from within there, providing that you altered the scope of the parserTimer itself to make it an instance variable. I don't see a problem with that provided that you access it only from within init and destroy.
The servlet engine is free to unload the servlet whenever it sees fit, but in pratice I'm only ever seen it called as the servlet engine is stopped - other people may have other experiences of this though that might prove me wrong.
