Initializing Parameters

I'm writing a web application using Tomcat and Struts. I'm trying to
place parameters in my web.xml file for use in the application (DB
username, smtp server, etc).  I'm having trouble finding examples of the
use of context-params and init-params, which one do I use? 
 
I think I use context-params but I have an HttpServletRequest which
doesn't have the getInitParamater() method. is that even the right
direction? 
 
I'm just looking for a way to pass some variables in without have to
recompile every time I change one.  Any help in the way of example code
would be much appreciated.
 
Thanks, 
Andy