Are Java EE 5, 6, & 7 compatible application servers compatible with J2EE?

Question

There are J2EE compatible application servers and also Java EE 5, 6, 7 compatible application servers. You will find them in the below link. Link: http://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition#Certified_application_servers

My question is:

Are Java EE 5, 6, & 7 compatible application servers compatible with J2EE ? Is there backward compatibility always?

Thanks.

Answer 1

always? no. The deployment profiles introduced in Java EE 6 (or was it 5) mean that it is possible to deploy a server that does not support the complete API.
Which means that not all Java EE applications (or J2EE) will work on that deployment.
That's not in accordance with the J2EE (1.4 or earlier) specifications, which didn't have such a thing.

In general though, a full deployment should be backwards compatible, as the APIs themselves are designed to be such.
But there's of course no guarantee. Deprecated functions might be implemented in a Java EE implementation to do something different from their original implementation in older versions (like do nothing, which I think is the recommended way to go for some old calls that had serious security implications).