Jazoon, Day 2: XWiki

24. June, 2009

I’m a huge fan of wikis. Not necessarily MediaWiki (holy ugly, Batman, the syntax!). I dig MoinMoin. I just heard the talk by Vincent Massol about next generation wikis. Okay, I can hear you moan under the load of buzzwords but give me a moment. XWiki looks really promising.

Wikis basically allow to publish mostly unstructured data. I say “mostly” because wikis give them some structure but not (too) much: You can organize it in pages and put it into context (by linking between the pages). Often, this is enough. But recently, MediaWiki has started to add support for structured data. See that infobox in the top left corner? But that’s just half-hearted.

XWiki takes this one step further. XWiki, as I understand it, is a framework of loosely coupled components which allow you to create a wiki. The default one is pretty good, too, so most of the time, you won’t even get into this. The cool part about XWiki is that you can define a class inside of it. Let me repeat: You can create a page (like a normal text page) that XWiki will treat as a class definition. So this class gets versioned, etc. You can then add attributes as you like.

After that, you can create instances of this class. The instances are again wiki pages. You can even use more than a single instance on a page, for example, you can have several tag instances and a single person instance. Instances are versioned, too. Of course they are, this is a wiki!

Now you need to display that data. You can use Velocity or Groovy for that. And guess what, the view is … a wiki page. So your designers can create a beautiful look for your the boring raw data. With versions and comments and everything. While some other guys are adding data to the system.

In “normal” wiki pages, you can reference these instances and render them using such a template. The same is true for editors. With a few lines of code, you can create overview pages: All instances of a class or all instances with or without a certain property or you can use Groovy to do whatever you can think of.

Now imagine this: You have an existing database where your marketing guys can, say, plan the next campaign. They can use all the wiki features to collect ideas, filter and verify them, to come up with a really good plan. Some of that data needs to go into a corporate database. In former wikis, you’d have to use an external application, switch back and forth, curse a lot when they get out of sync.

With XWiki, you can finally annotate data in your corporate database with a wiki page, with all the power of a wiki and you can even display the data set in the wiki and edit it there. Granted, the data set won’t be versioned unless your corporate database allows that but it’s simple to do the versioning in the data access layer (for example, you can save all modifications in a log database).

Suddenly, possibilities open up.

Precompiling Custom JARs

24. June, 2009

Java 5 precompiles the rt.jar to a file with the JIT when you start it the first time. This is mostly to improve startup times; it takes only a few moments and is much more efficient than running the JIT when a class has been used more than N times. Next time the class is requested, the VM skips the bytecode loading and directly pulls in the precompiled binary which is already optimized for your CPU.

My idea is to open this process for custom JARs. Any big Java app loads heaps of external JARs and that takes time – often a lot of time. JARs would need to supply a special META-INF file which contains a UUID or a checksum from which the VM can conclude whether the JAR has changed or not.

The first time the JAR shows up in the classpath, the JIT precompiler would convert it, save the result in the cache. Next time, the META-INF file would be read, and the bytecode would be ignored. I’ll open a enhancement request in OpenJDK 7. If you like the idea, please support it.