System Mobile

Avoid an MVEL Bug In Drools Snapshots

nick — Wed, 20 Jan 2010 22:21:13 +0000

If you’re working with Drools trunk snapshots, you may be tripping over a bug in MVEL that caused me to lose about a day. On the RHS (right-hand side, the consequence) of my rule I had the following:

$queryResult.addResult(new Result($obj));

Which resulted in this error: [Error: unable to access property (null parent): $obj]

However, if I call an accessor or otherwise do something with the object before passing it off to the constructor, it works fine:

$obj.getName(); $queryResult.addResult(new Result($obj));

Right now this appears to be a problem in MVEL, but I don’t know enough about the internals of Drools of MVEL to say for sure. Ideally this workaround will keep you moving forward.

VMware and SpringSource - Why Bother?

nick — Mon, 10 Aug 2009 20:54:57 +0000

Monday saw the rather surprising announcement that VMware is acquiring SpringSource for about $420m all in. After the initial shock wore off, the next question had to be: Why bother acquiring SpringSource in the first place? According to the press release:

VMware and SpringSource plan to deliver compelling new solutions that enable companies to more efficiently build, run and manage applications within both internal and external cloud architectures.

So VMware is going to attempt to use SpringSource’s code to virtualize application deployments and management. Given Spring’s hooks into several application frameworks, it’s certainly possible but by no means guaranteed.

With a recent stock downgrade (from Buy to Underperform), VMware has to make something happen quickly to justify spending over $400m for glorified middleware.

VMware shares are down just over 2% today.

Querying XML with eXist

nick — Sat, 08 Aug 2009 02:48:01 +0000

Recently I needed to be able to be able to query a bunch of XML files using XQuery. I looked at some options like CouchDB but ultimately I needed a database of some sort that had native support for XQuery. While it looks like you can add on or hack in XQuery support to CouchDB, I preferred to keep things simple and went with eXist.

eXist allows you to store XML documents, with supporting DTDs and schemas, and access the collections using various mechanisms like REST or WebDAV. Once you have a number of XML documents in your repository, issuing an XQuery using the REST interface is pretty simple:

<?xml version="1.0" encoding="UTF-8"?> <query xmlns="http://exist.sourceforge.net/NS/exist" xmlns:foo="http://www.systemmobile.com/2006-05-05/foo"> <text> <![CDATA[ for $i in /foo:Bar return <result>{$i/@priority}</result> ]]> </text> </query>

The above query will return a something like:

<exist:result xmlns:exist="http://exist.sourceforge.net/NS/exist" exist:hits="24" exist:start="1" exist:count="10"> <result priority="1"/> <result priority="1"/> <result priority="1"/> <result priority="1"/> <result priority="1"/> <result priority="1"/> <result priority="1"/> <result priority="1"/> <result priority="1"/> <result priority="1"/> </exist:result>

You can learn more about XQuery’s FLWOR structure here.

But eXist is more than just an XML store. By supporting XPath, XUpdate and XQuery Update, as well as custom extensions, eXist can be an application platform. I’m looking forward to working with XForms and Wicket in the future and I believe eXist will play heavily in that.

Wicket RefCard Released

nick — Wed, 29 Jul 2009 18:54:53 +0000

Congrats to Andrew over at Mystic Coders for releasing his Wicket reference card over at DZone.

Of course, I’m probably going to take his refcard text and work it into WicketForge.

At long last, an excellent JAXB tutorial

nick — Tue, 24 Mar 2009 18:57:45 +0000

Like it or not, if you’re writing code today you’re going to have to deal with consuming and producing XML. From my experience, one of the best options to manage the heavy lifting surrounding XML. However finding useful information on JAXB is difficult, with various forum posts and mailing lists, most information is out of date. Luckily Wolfgang Laun has created an outstanding tutorial. Wolfgang’s tutorial is possibly the most comprehensive (and most current) information on every aspect of JAXB. I highly recommend it both as a getting started guide and a reference.