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:
https://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.