Benefits (and tips) of an upgrade from JBoss 4.2.x to JBoss 5.x, 6.x, 7.x and WildFly 8.x?
Please assume that I do not need to worry about development time and costs: I am interested in general technical benefits (improved performance? improved APIs?) and new features.
I am currently working on products using 4.2.x, and we consider a major shift for versions that are a long time ahead and need to converge.
I had a brief look at the release notes of each version and some articles about each release for 5.x, 6.x, 7.x and 8.x. But I would be glad to have first-hand feedback from people who have made the switch.
I noticed there are some important changes surrounding messaging (switching from JBoss MQ to JBoss Messenging), and that for JBoss 7.x it seems to change a fair bit its configuration layer. Then there's a lot more going on when switching to JBoss/WildFly 8.x.
Please recommend good articles pointing at pitfalls if you can. I found a few for migrations to JBoss 5.x, but not that many for 6.x or even 7.x, and someone else is evaluating 8.x for us now. Feel free to recommend alternatives as well if you think they are relevant, though I'd prefer to focus only on JBoss.
For information, we use a mix of JPF- and OSGi-enabled (using Eclipse Equinox) plugin-based systems, with clients developed in Swing (some deployed via WebStart).
Update: Though this question brought some great answers already, I think it deserves an update for WildFly (and actually, our internal projects delayed making the switch from 4.2.x to 7.x as originally planned to wait for WildFly). New thoughts and answers are welcome.
Answer
I've upgraded from JBoss 4 to 5 and from experience the following are the most important to note:
- JBoss 5 (and 6 and 7) are not as forgiving as JBoss 4 with XML files. You must make sure that all your deployment descriptor XML files are valid. You may be using DTDs in some files - I recommend upgrading these to use XML schema instead.
- Some libraries may cause incompatibilities. This can be particularly true if you access web services and/or do XML parsing
- If you precompile your JSPs in JBoss 4, you probably won't be able to in JBoss 6/7.
- JBoss 4 and 5 use different message queue implementations. If you have any message queues or topics defined you will need to redefine them.
- JBoss TreeCache is no longer used. If you use this for caching purposes, you will need to change to use the new JBoss cache instead.
- JBoss 5 security is different. If your remote clients require secured access to JBoss, you will need to configure them differently.
Some useful resources are:
http://java.dzone.com/articles/migrating-jboss-4-jboss-5 http://venugopaal.wordpress.com/2009/02/02/jboss405-to-jboss-5ga
Officially JBoss 6 is only certified for the Java EE Web Profile, so if you use "legacy" features such as EJB 2.x, they will potentially not be supported in the future. Depending on the lifecycle of your application, this may or may not be a problem. JBoss 6 currently supports EJB2.1 fully, but it is not certified against this.
I have also found that JBoss 5 handles memory a lot better that JBoss 4. With JBoss 4 I see a lot more PermGen errors than I do with JBoss 5.