Building Maintainable Web Applications

The critical requirement for building maintainable web applications is appropriate separation of layers of the application. Slightly simplified, a web application typically consists of the following layers:
a web view layer: this consists of web page templates, or some other view technology, whose responsibility it is to supply input data to the server application, and to present the results of this interaction

• a presentation logic layer: this part of the application controls the presentation work flow: which pages get displayed, how they are initially populated, and how and when transitions between view layer components occur
• a business layer: this part of the application controls the business processing logic. It works completely independently of the web layer
• a data access layer: responsible for retrieving and storing data in the application database. Accessed from the business layer

When writing maintainable web applications, it is very important to separate the web view and presentation logic layers. This minimises the impact of changes to the view layer on the presentation logic layer, and vice versa.

This kind of separation can be enforced through the use of a model view controller (MVC) framework, of which numerous excellent open source implementations are available from the Java open source community. The best known of these is Apache Struts, although Spring also has a powerful web MVC framework. We can work with these and several others in building maintainable web applications.