Tutorials : Converting XML documents to Java objects with Castor XML :

Converting XML documents to Java objects with Castor XML

by Keld H. Hansen

Introduction

In my two recent articles, "Mapping Java Objects to a Database with Castor-JDO" and "Cultivating your Relationship with Castor-JDO", I've presented Castor JDO, a framework for mapping Java objects to a relational database. The Castor project also houses another, very popular mapping framework, Castor XML, which is used to map Java objects to XML documents. In this article we'll look into how Castor XML could be yet another useful item in your toolbox.

Why would you want to use Castor XML as the bridge to an XML file when you have several other tools like JDOM, SAX, and dom4j that will do the same thing? The answer is that Castor is able to elegantly map XML documents directly to instances of your own Java classes. In other words, if someone comes along with an XML document containing "customer data": name, address and so on, and you've got some Java classes that can hold name, addresses etc, then you'd normally be able to specify a mapping (through an XML mapping file) that would allow transformations from the XML document to your classes and back again, without having to make modifications to your Java code.              

Castor XML can do more than this. If you only have an XML-document, whose contents you would like to work with in your Java program, then Castor is also able to create the necessary Java classes for you.    

I'll illustrate this by taking a deployment descriptor for a web application, and then let Castor create the Java code needed for processing it. The deployment descriptor file is most often named web.xml, and if you're running a web server (like Tomcat) on your computer, then go and search for this file, and you'll probably find several, since there's one for each application/project on your server. 

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