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Solve your servlet-based presentation problems

Various techniques for implementing content presentation in thin-client applications

By Kevin Unger, JavaWorld.com, 11/03/00

Sun Microsystems created Java servlet technology, and it was good. (See Resources.) All subsequent Java server techniques have been based on servlets. And while nobody argues against servlets' efficacy, the debate rages on over which follow-on technologies (if any) are best for solving Web-based presentation problems. Those problems include:

1. Separating presentation (HTML) from content generation code (code that accesses databases and generates XML documents, result-set data structures, Java object data, and so on)
2. Maintaining consistency with the modern component-based software construction paradigm, to leverage modularization and code reuse
3. Reuse and nesting of markup in different page contexts (templating)
4. Minimizing the learning curve for new scripting languages and tag vocabularies, and maximizing their compatibility with HTML authoring tools

Combining code and presentation obfuscates the design intent behind both elements, and encourages the designer/programmer to design the software and the page simultaneously -- two very distinct activities. Or, even worse, if separate page designers and programmers work on the site, they won't be able to work simultaneously without breaking each other's code.

Disregard for object-oriented software-component construction and the inability to reuse and nest markup blocks are closely related to the blending of markup with content generation code. Mingling code and markup means specific content generation code is hardwired to specific formatting. That limits your ability to build encapsulated objects for generating content. There is a similar problem for presentation components (templates): if the presentation is mingled with the content generation code, you have little chance of reusing or nesting page elements.

The techniques discussed in this article (besides raw servlets) enhance HTML documents by employing scripting languages, sets of custom markup tags, and automatic Java class generation to help solve the first three problems in the above list. If it is too difficult for nonprogrammers to learn to use these tools, then we must still deal with the problem of programmers being forced to become page designers. Page designers rely on HTML authoring tools, so new tags and scripts should be as friendly to authoring tools as possible.

I did not include performance and scalability in the list of problems, but they are primary issues. Commercial servlet engines generally provide excellent performance and most now offer high-end scalability features, so most servlet-based presentation solutions will perform and scale well. However, some techniques add loads to the server, such as realtime XML parsing and XSL processing. The performance-analysis details of adding those loads are beyond the scope of this article.

The following discussion describes some servlet-based Webpage-presentation techniques, with respect to the above list of problems. Specifically, this article discusses the main techniques for solving presentation problems by focusing on a small, representative sampling of systems that implement them. A raft of servlet-based templating engines and server-side Java application frameworks are available or in development, but are not mentioned here.

 

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