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Converting XML to JavaBeans with XMLBeans

Introduction

A month ago or so one of my colleagues told me about a new XML- to-JavaBeans conversion tool called XMLBeans that he had success with. He even compared it to Castor-XML, a conversion tool many programmers have been using for a long time, and have been extremely satisfied with. A couple of weeks ago I had the chance to look more into this new tool, and in this article I'll try to sum up my findings.

XMLBeans is developed by BEA Systems, and was donated as an open source software to the Apache Foundation in December 2003. Like Castor, XMLBeans takes an XML schema file and produces a set of Java classes that can be used to convert ("marshal") an XML instance that conforms to the schema. Reading the specs for XMLBeans the first thing that strikes one is its ability to handle any (!) XML schema. The other thing that made me really interested was the fact that XMLBeans preserves the underlying XML document and schema structure, thus making it possible to use query languages like XQuery (see however my discouraging findings described later) on the document structure. Finally I really liked that the code generation tool would make me a jar-file ready for use in my programs.

If you're not interested yet, then I suggest you read the XMLBeans FAQ from BEA. It gives a lot of good, relevant information that I'm sure will make you curious about this new tool.

This article will show you how to:

install XMLBeans
generate Java code and classes from schemas
run some simple programs
validate an XML file against a schema

Finally I'll show how you could wrap the XMLBeans tool so it can be replaced by any other marshalling tool. This is always a nice thing to do, and the technique I'll show is quite general, and not related to XML marshalling.

In the resources section you'll find pointers to newsgroups and some interesting discussions about XMLBeans and its relations to other tools and standards.

Install XMLBeans

Here's a link to BEA Systems from where you may download XMLBeans. It's not available yet from the official Apache site because at the time of this writing it's still in the "incubation process" at Apache. Nonetheless, you may find zip files on several Apache mirror sites if you search for "apache xmlbeans" on the web. I've not compared the BEA and Apache downloads in detail, and my experience with XMLBeans comes from using the version from BEA. By the time you read this article, XMLBeans might be available from the official Apache XMLBeans site.

The XMLBeans.zip from BEA contains all you need, documentation, examples, utilities and a jar file with the general classes. I assume that you the reader have available a JDK 1.4.x. The steps to follow to install XMLBeans are these:

Unzip the download in a directory, for example c:\xmlbeans,
Set the environment variable XMLBEANDIR to point to the directory containing the xbean.jar file, e.g. on Windows:
set XMLBEANDIR=c:\xmlbeans\xkit\lib
To generate the Java classes for your schema run the scomp utility located in the bin folder. For convenience add this folder to your PATH:
set PATH=%PATH%;c:\xmlbeans\xkit\bin
Try to enter "scomp". This will show you the usage information for scomp.

This completes the installation!

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