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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

Page 2 of 6

• HTML: Helps create HTML tags, particularly by filling out HTML forms with data from the model.
• Bean: Manipulates beans.
• Logic: Implements logic constructs based on bean values.
• Template: Handles page templates.

With the Struts tag libraries, you can usually avoid using any Java code in the view.

Struts/JSP drawbacks

While the Struts/JSP approach features many advantages over other models, it exhibits several drawbacks:

• As in Model 1's case, nothing prevents a developer from embedding application logic into the JSP. Experience shows that many developers actually fall into that trap, often to perform a quick fix. This can lead to applications that are hard to understand and maintain.
• The JSP syntax is not XML compliant and therefore fails to guarantee that resulting XML or HTML documents will be well formed.
• The developer must learn new APIs -- the Struts tag libraries. Experience shows that gaining an understanding of the Struts tag libraries, particularly the bean and HTML libraries, can take a long time.
• You can't implement a real processing pipeline in the view with JSP. Only basic includes and forwards are possible, effectively limiting the view's flexibility. For example, separating layout and style proves difficult.
• With JSPs, you must recompile after every change, which can be time consuming. Just ask any JSP developer waiting for page compilation after every mouse click.

The solution to these problems must:

• Restrict the visibility in the view to the model and some well-defined context information, such as resources.
• Enforce well-formed XML and HTML.
• Leverage existing languages or APIs.
• Ease the separation of different view aspects, like layout and style.
• Allow for a faster development cycle.

As detailed, the Model 2 technology currently features many issues that must be addressed. We believe the lightweight framework detailed below, based on an unmodified version of Struts and XSLT, exceeds the given requirements. We call the new architecture Model 2X.

Model 2X: Architecture overview

Model 2X is the symbiosis between Struts and XSLT. Model 2X uses the Struts model (its controller servlet), but the view implementation uses XSLT and beans serialized into XML instead of JSPs.

What is XSLT?

XSLT is a functional language designed to perform transformations on XML documents. It is part of a stylesheet language for XML known as XSL. XSLT uses XPath, an expression language that accesses or refers to parts of an XML document. In addition to XML dialects such as XHTML, XSL/FO (formatting objects), or SVG (Scalable Vector Graphics), XSLT can output any text format, including HTML or CSV (comma-separated values). Also part of the XSL specification, the XSL/FO language displays elements on a page. Its main application: generating PDF documents.

Integrate XSLT with Struts

The first approach to integrating XSLT with Struts is to call an XSLT transformer from within a JSP. You do that with a tag library -- the Jakarta Project's XSL tag library, for example. You now generate XML, instead of HTML, in the JSP. Thanks to an XSLT stylesheet, the XML then transforms into HTML or other formats. However, this transformation requires changes to Struts itself.