The main entry point to Nucleus is though its request-handling facilities. When a web application running Nucleus receives an HTTP request, it invokes a series of servlets and servlet filters that process the request and construct the response:
When a user requests a page, that request is sent to the web server as a stream of information that the web server parses and holds in an
HTTPServletRequestobject.The web server passes the
HTTPServletRequestto the application server, which it wraps in its own flavor of request around the generic one before passing it to the web application.Any custom J2EE servlets are processed.
The web application calls the
PageFilterresource and starts the servlet pipeline.The request is passed on to a pipeline of servlets. Each servlet available to the pipeline is designed to insert itself into the pipeline when a given request includes the information that it processes. So, a unique pipeline is constructed for each request. If you created any custom servlets and they apply to the current request, they are executed now.
If you created custom filters and a JSP is being requested, they execute after the last pipeline servlet, but before the request returns to the application server.
After the servlet pipeline reaches the end, it returns the request to the application server for final processing (executing the servlet representation of the page).
The following figure illustrates this process:
For more information about request handling pipelines, see the Request Handling with Servlet Pipelines chapter in this guide.
