Request Process Flow
This page describes the process used by Tomcat to handle an incoming request. This process is largely defined by the Servlet Specification, which outlines the order of events that must take place.
A UML sequence diagram of the request process is available here.
The Servlet Specification provides many opportunities for listening in (using Listeners) or modiying (using Filters) the request handling process even before the request arrives at the servlet that will handle it.