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Boost Struts with XSLT and XML

An introduction to Model 2X

By Julien Mercay and Gilbert Bouzeid, JavaWorld.com, 02/01/02

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Since the Java Servlet API's inception, developers have used diverse technologies to develop Web applications in Java. Recently, developers have started to recognize the merits of Model 2, a scheme derived from the Model-View-Controller (MVC) paradigm. Model 2's benefits include an improved separation of the application logic and presentation layers. Struts, built on top of Model 2, additionally offers Java developers a generic controller servlet, centralized configuration, resource management, and error handling.

In this article, we introduce Model 2X, a scheme that further enhances Struts. By replacing JSPs (JavaServer Pages) with XML and XSLT (Extensible Stylesheet Language Transformations), Model 2X offers an even better approach to separating logic and presentation. We start with an introduction to Model 1 and Model 2, describe how Struts implements MVC, and finally show how XML and XSLT can be used to improve the existing models.

Model 1

Understanding Model 1 is crucial to understanding the subsequent architectures we discuss in this article. Model 1's cornerstone is the JSP file, which extracts parameters from an HTTP request, calls the required business logic, handles the HTTP session, and then generates HTML.

A complete Model 1 application is composed of a collection of JSP files, mostly independent of each other, and, optionally, a collection of support classes and other components. Earlier technologies, such as ASPs (Active Server Pages) and PHP (hypertext preprocessor), used this same model.

Model 1's major, and possibly only, benefit: simplicity. However, Model 1 encourages the developer to mix business logic and presentation logic, a significant drawback. While this model is appropriate for creating small applications, complex application development with Model 1 can become difficult to manage.

Model 2, MVC, and Struts/JSP

Object-oriented paradigms in the form of the MVC architecture rescued the JSP and servlet world by defining Model 2. Figure 1 illustrates MVC's three parts and their implementation in Struts/JSP.

Figure 1. Model 2

Controller

As Figure 1illustrates, the Struts' main component is a generic controller servlet. The Struts controller provides the initial entry point for all HTTP requests routed to Struts. It interprets and dispatches all requests to individual actions implemented by the developer as subclasses of the Struts Action class. It also automatically fills out form beans from request parameters. Individual actions implement core business logic by, for example, making EJB (Enterprise JavaBean) calls, and access the model through JavaBeans. An XML file that maps request URIs to actions and form classes configures the controller servlet.

Model

The model takes the form of one or several JavaBeans. Those beans fall into three categories:

  • Form beans hold either the data the user entered in HTML forms or, more generally, any attribute passed either on the URL or in a POST. For instance, a form bean for a login page could have two properties: login and password. Form beans extend the Struts ActionForm class.
  • Request beans hold information needed to generate the HTML page. In the case of a bank account statement page, a request bean would have properties with information about the account as well as a transaction bean collection detailing the most recent transactions to display.
  • Session beans hold session information that persists between two HTTP requests by the same user.


View

The controller servlet forwards a request to a JSP implementing the view. The JSP can access the form, request, and session beans and outputs a result document (usually an HTML document) sent to the client. Struts provides four JSP tag libraries:

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