This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
The contextpath is necessary for identifying the application (but can be omitted if the app is the root application), and profile can be a servlet mapping that invokes a servlet that will look up the user's profile and forward to a JSp for displaying it.
Within the servlet, the username part of the URL can be retrieved using the path info methods on the request.