Basic Components of Struts

This article describes the basic components of Struts and it is the continuation of the Introduction To Struts. libraries for working with view technologies other than JSP, and so on.

The Struts framework is a rich collection of Java libraries and can be broken down into the following major pieces:

• Base framework
• JSP tag libraries
• Tiles plugin
• Validator plugin

A brief description of each follows.

Base Framework
The base framework provides the core MVC functionality and is comprised of the building blocks for your application. At the foundation of the base framework is the Controller servlet: ActionServlet. The rest of the base framework is comprised of base classes that your application will extend and several utility classes. Most prominent among the base classes are the Action and ActionForm classes. These two classes are used extensively in all Struts applications. Action classes are used by ActionServlet to process specific requests. ActionForm classes are used to capture data from HTML forms and to be a conduit of data back to the View layer for page generation.

JSP Tag Libraries
Struts comes packaged with several JSP tag libraries for assisting with programming the View logic in JSPs. JSP tag libraries enable JSP authors to use HTML-like tags to represent functionality that is defined by a Java class.

Following is a listing of the libraries and their purpose:

• HTML Used to generate HTML forms that interact with the Struts APIs.
• Bean Used to work with Java bean objects in JSPs, such as accessing bean values.
• Logic Used to cleanly implement simple conditional logic in JSPs.
• Nested Used to allow arbitrary levels of nesting of the HTML, Bean, and Logic tags that otherwise do not work.

Tiles Plugin
Struts comes packaged with the Tiles subframework. Tiles is a rich JSP templating framework that facilitates the reuse of presentation (HTML) code. With Tiles, JSP pages can be broken up into individual ’tiles’ or pieces and then glued together to create one cohesive page. Similar to the design principles that the core Struts framework is built on, Tiles provides excellent reuse of View code. As of Struts 1.1, Tiles is part of and packaged with the core Struts download. Prior to Struts 1.1, Tiles was a third-party add-on, but has since been contributed to the project and is now more tightly integrated.

Validator Plugin
Struts comes packaged, as of version 1.1, with the Validator subframework for performing data validation. Validator provides a rich framework for performing data validation on both the server side and client side (browser). Each validation is configured in an outside XML file so that validations can easily be added to and removed from an application declaratively versus being hard-coded into the application. Similar to Tiles, prior to Struts 1.1, Validator was a third-party add-on, but has since been included in the project and is more tightly integrated.