JavaServer Pages, 3rd Edition

Struts Request Processing Overview

With power comes complexity, unfortunately. Before jumping into the details, here’s a brief summary of the parts of Struts I use for the Project Billboard application.

The Struts servlet delegates the real processing of requests to classes that extends the Struts Action class. The main method in this class is the perform( ) method. For each type of request the application supports, you create a separate action class and provide the code for processing this request type in the perform( ) method. Figure 19-3 shows the action classes used by the Project Billboard application.

Figure 19-3. Controller split over dispatcher servlet and action classes

The Struts servlet uses parts of the request URI to figure out which type of request it is, locates the corresponding action class (using configuration information), and invokes the perform( ) method. Note that this method doesn’t render a response; it takes care of business logic only, for instance, updating a database. The perform( ) method returns a Struts ActionForward instance, containing information about the JSP page that should be invoked to render the response. The page is identified by a logical name (errorPage, mainPage, etc.), mapped to the real page path in a configuration file. The page flow can therefore be controlled, at least to some extent, by reconfiguration instead of code changes.