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20.8 The MVC Paradigm for Web Applications
MVC is an acronym for
Model-View-Controller, a powerful
object-oriented architecture used for graphical user interfaces and
also adopted for web applications. The Model is the object or objects
upon which that application acts: they are the data. The objects that
make up the Model are the core classes of the application. The View
is the object or objects that display the model to the user. The
Controller is the object that ties everything together, creating view
objects for the model and translating the user's
interactions with the view into modifications of the model.In a Java web application, the Controller is a special-purpose
servlet and the View, or Views, are JSP pages. The
Controller servlet handles all incoming
requests, examines them, takes any necessary actions on the Model,
and then dispatches the request to an appropriate JSP page, which
displays a response to the user. The Model for a web application can
be any kind of object, although, by convention, Model objects follow
JavaBeans naming conventions with get/set property accessor methods.The examples that follow constitute a simple web application, named
ListManager, for managing a mailing list. As
pictured in Figure 20-2, this web application allows
users to subscribe to, set delivery preferences for, or unsubscribe
from a mailing list. (The example program is not capable of actually
sending email to the list subscribers, however.) In the following
sections we'll see the Model classes, the Controller
servlet, and the JSP views for this web application. Because the
Model, Controller, and Views are interdependent, you may need to read
through these examples twice in order to understand all the details.
Figure 20-2. The ListManager web application
