Java Enterprise in a Nutshell, Third Edition

The Struts Controller

In a moment we will discuss the Struts approach to the MVC controller and then provide detail on the building-block classes, org.apache.struts.action.Action and org.apache.struts.action.ActionForm. But first we should take a step back and look at the nail for which Struts is attempting to be the hammer. In many web applications, the basic HTTP interaction is not especially complicated. An HTTP request includes at least the name of a resource and zero or more parameters. Based on the name of the resource and the parameters, control must be handed off to specialized code that performs an action. The action determines what response is appropriate; this HTTP response is then encoded and returned to the requester, typically with HTML as the message body. So far, so good.

But in ad hoc web programming, it is all too easy to handle each of these tasks in an idiosyncratic way. For example, a developer might write a servlet to handle a request and might create his own methods and conventions for validating parameters (ensuring that certain parameters are syntactically valid phone numbers, perhaps). Meanwhile, another coder, working primarily on GET requests, writes her own method for validating parameters. Clearly, there are organizational and maintenance issues here with the existence of two modules doing similar tasks, maintained by two different people. But the larger issue is that there are well-known patterns for handling such minutiae—and if handled once, and well, ...