After three years of work, Red Hat has finally completed the first -- but probably not the final -- release candidate of JBoss Application Server (AS) 5.0, a long delayed Java-based product built around a "Lego block" approach.

Initially slated for general availability (GA) during the first half of last year, JBoss Application Server Version 5.0 first entered beta back in November 2006.

In a recent blog entry, JBoss CTO Sacha Labourey attributed the ongoing postponements to a major redesign aimed at greater modularity and manageability across the application server's three-layer software architecture.

"The idea was to move to a much more generic micro-kernel architecture that could suit multiple 'personalities' (OSGi, JMX, pure POJO, etc.) and fully componentize (through APIs and SPIs) and aspectize our AS down to the bare minimum 'Lego blocks,'" Labourey wrote in his blog. "Also, we wanted our new runtime to have full manageability features as a core aspect, not as an afterthought. The magnitude of these core changes came at the expenses of a reliable roadmap -- hence the multiple delays in releasing JBoss AS 5.0." The three software layers of JBoss AS include a JVM (Java Virtual Machine) runtime, core middleware services, and a programming model/API and language layer. Version 5.0 is the first release that cleanly separates those three layers, he said. A kernel known as JBoss Microcontainer "abstracts us from the runtime environment, and our core enterprise services have been completely componentized and aspectized so they can be fully leveraged from any higher level framework/API/language." But the development work hasn't constituted just a "fancy engineering exercise," according to Labourey. "This investment will have a drastic impact on the overall JBoss Middleware offering, its longevity and its ability to adapt to market changes," he insisted.

Still, the rest of the enterprise software market hasn't exactly stood still, either, over the past three years -- even beyond all the changes that have happened on the opposing Microsoft .NET side, including Microsoft's extensive interoperability deal with Red Hat rival Novell.

Oracle's purchase of BEA Systems has thrown some confusion around the future of BEA's AS software, traditionally a competitor against JBoss. Meanwhile, though, SpringSource released a major new contender in the open source Java arena in April. Labourey hinted in his blog, however, that JBoss AS Version 5.0 could be ready for GA as early as late this summer. Intimating that a second release candidate will be available by mid-August, he added that "GA should follow closely thereafter."