J2EE Design Patterns

Name

Model-View-Controller

Also Known As

MVC, Model 2

Goal

Separate presentation tier into self-contained, reusable pieces (Figure A-5).

Figure A-5. Classes in the MVC pattern

Participants

Model

Stores application state data.

Views

Stateless pages that transform model data into a form appropriate for display to the user, such as HTML, WAP or XML.

Controllers

Process user input, update the model, and choose views (Figure A-6).

Figure A-6. Interactions in the MVC pattern

Interactions

The controller receives the user input, and translates it into appropriate updates to the model. The model applies business rules and stores the data persistently, either locally, in the business tier, or using some other remote persistence mechanism. Based on the model changes and user input, the controller chooses a view. The view transforms the updated model data into a form suitable for the user.

Notes

In J2EE, the model is typically implemented as JavaBeans or EJBs. The views may be JSPs, static HTML pages, or even servlets. The controller is usually a servlet.