This is a Java servlet filter (as per Servlet API 2.3). This filter lets you calculate resource usage statistics for your users. BillingFilter counts for the each session three parameters: how many requests have been proceeded, how many bytes have been transferred to user and how many milliseconds of processor time have been spend for those requests. So you may use this filter for some billing system, especially for some wireless applications.

Try it Out: http://www.servletsuite.com/servlets/billflt.htm