Introduction to Model View Controller Architecture
by, 11-14-2011 at 06:51 PM (783 Views)
Designing large sized enterprise applications is a difficult task because the code maintenance becomes difficult as the size of application goes. Model View Controller Architecture presents a solution to this. In this post, I will introduce you to MVC.
Web applications based on JavaServer Pages sometimes mix database code, page design code, and control flow code. In practice, we find that unless these concerns are separated, larger applications become difficult to maintain. One way to separate concerns in a software application is to use a Model-View-Controller (MVC) architecture.
Model-view-controller (MVC) is an architectural pattern used in software engineering. In complex computer applications that present a large amount of data to the user, a developer often wishes to separate data (model) and user interface (view) concerns, so that changes to the user interface will not affect data handling, and that the data can be reorganized without changing the user interface. The model-view-controller solves this problem by decoupling data access and business logic from data presentation and user interaction, by introducing an intermediate component: the controller.
In (classic or original) MVC, the View updates itself from the Model, via the "Observer" pattern. The original MVC pattern is like a closed loop: The View talks to the Controller, which talks to the Model, which talks to the View. But, a direct link between the Model and the View is not practical for web applications, and we modify the classic MVC arrangement so that it would look less like a loop and more like a horseshoe with the controller in the middle.
In the MVC/Model 2 design pattern, application flow is mediated by a central Controller. The Controller delegates requests - in our case, HTTP requests - to an appropriate handler. The handlers are tied to a Model, and each handler acts as an adapter between the request and the Model. The Model represents, or encapsulates, an application's business logic or state. Control is usually then forwarded back through the Controller to the appropriate View. The forwarding can be determined by consulting a set of mappings, usually loaded from a database or configuration file. This provides a loose coupling between the View and Model, which can make applications significantly easier to create and maintain.
The framework provides the control layer for a Model 2 web applications. Developers can use this layer with other standard technologies to build the business, data access, and presentation layers.