Way to keep minimal application-server dependency?

What is the best (easiest, most seamless) way to build a Java app while relying as little as possible on the actual application-server used in deployment?

For example, say I want to deploy on Apache Geronimo, and later want to use GlassFish, how difficult would the transition be? What is the best way to abstract the use of each app server?

Excuse my ignorance, I'm relatively new to Java development. I want to start a new开发者_C百科 project, but am unsure on whether to use separate APIs for the functionality I need or develop on top of a chosen app-server from the start.

Thanks for your help,

Ivan

Without getting into too much details, even though you can write bare-bones Java EE code, the configuration around it is not very simple. Each application server has its own set of configuration files and naming conventions (for example, the format for specifying the location of the AS is different in IBM WAS and in JBOSS). Though these are not very important for application development, once you get to the deployment phase, these will become important. As far as the libraries and your code is concerned as long as you stick to EJB standards you will be able to run your application on majority of the application servers (I know of WAS and JBoss - the code that I wrote didn't have to change for these servers; the configuration though, well that was a different beast !).

Follow Java EE specification as much as possible, while follow server specification least as possible.

If we try to find out what are in common among there Java EE application servers(JBoss, WAS...), answer is Java EE specification which server vendors must follow. If you have 2 solutions on a Java EE problem, you could check which solution comply with Java EE specification better rather than server specification.

From my experience with Jboss and Sun AS, you should just forget about AS-independency.

In sql, for example, you can do quite a lot without employing vendor-specific features. Well, it's not like that in Java EE. For Jboss and SAS even 'hello world' applications will require different configuration. And more application grows, more vendor-specific features you have to use.

In particular, if you look at official Sun Java EE tutorial, you'll find that it employs SAS-specific configuration files (sun-web.xml, sun-ejb-jar.xml, etc) from the very beginning.

But all above applies only if you use full range of Java EE features (like EJB, JMS, mbeans). I've found that if you just have servlets/jsps packaged in one war-archive, such application can still be very portable.

If you have the resources then consider developing and testing for several application servers instead of just your initial target one. This will allow you to - from the start - pinpoint things that need to be configurable and code accordingly.

Personally I would consider Glassfish 3.0.1 in such a situation as it is the reference implementation, so things should at least work there without any special efforts.