Newsletter sign-up
View all newsletters

Enterprise Java Newsletter
Stay up to date on the latest tutorials and Java community news posted on JavaWorld

Sponsored Links

Optimize with a SATA RAID Storage Solution
Range of capacities as low as $1250 per TB. Ideal if you currently rely on servers/disks/JBODs

JavaWorld.com > Java Standard Edition >

Generate JavaBean classes dynamically with XSLT

Use the XSLT processor as a powerful source code generator

By Victor Okunev, JavaWorld.com, 02/01/02

  • Print
  • Feedback
.

In some commercial software projects, you cannot afford to cast in stone the structure of business objects. For example, different companies may have different and even mutually exclusive requirements for Product bean properties. Without a proper framework in place, you may end up spending long hours customizing all your data structures, including classes, database tables, DTDs (document type definitions), and so on, for every new customer. Needless to say, you may soon find yourself with a pocketful of parallel software versions and a maintenance headache. How do you ensure that your design is flexible enough to satisfy varying business requirements without a need to do extra coding each time those requirements change?

In this article, I lay a foundation for a simple framework I successfully employed to build truly adaptive systems. It is based upon dynamic source code generation from a class's metadata maintained in a data dictionary. In the process, you'll get a refresher on JDBC (Java Database Connectivity) and JSPs (JavaServer Pages), and you'll also learn to generate source code with one of today's most fascinating XML-related technologies, XSLT (Extensible Stylesheet Language for Transformations).

Short design session

First, let's set up a simple hypothetical project to which we can apply all the wonderful techniques discussed here. The project will be an application geared towards a vertical market that has a Product concept in its business vocabulary. You can pick your own favorite business domain -- financial services, online retailing, or maybe even technical training; anything that uses a product. The system architecture is not a constraint either; it may range from a standalone application to a distributed n-tier system. In this article, we will concentrate on the business object design issues equally applicable in the wide array of different projects.

Since we won't design this application for a particular customer, we must make sure we know the business well enough to cover the most complex cases. To achieve that, we hire the best domain experts, run a few CRC (class-responsibility-collaboration) sessions, chart several use cases, and eventually assemble a clear understanding of a Product concept, among many others. With that information on hand, we can build a conceptual business domain model that includes our perfect Product bean depicted below:

Product
code: int
name: String
testedOnAnimals: boolean
availableSince: java.util.Date


This is roughly what we do in real projects before the actual coding, especially if we adhere to a good software development process.

Traditional implementation



Now we can implement the construction phase, where we craft the Product bean's Java code. In Java terms, a bean is a reusable component from either the JavaBean or the Enterprise JavaBean (EJB) frameworks. Despite many significant differences between the two kinds of beans, there are also similarities. For example, they share the notion of a bean property. The bean property is based on the standard Java naming convention for the pair of accessor methods. Thus, if the bean has a nonindexed property code, it is assumed that it provides the writer and reader methods setCode() and getCode(), respectively. The reader method for the boolean type property would be isCode(). For an indexed property, the bean is assumed to possess two sets of setCode() and getCode() methods, one of which would be indexed while the other would deal with the whole array. The java.beans.Introspector uses the same rule set applied in reverse to dynamically analyze the bean class and discover the set of exposed bean properties on the fly.

  • Print
  • Feedback

Resources