Is there any tool or set of guidelines to migrate application using Spring, from Tomcat 6.0.35 to JBoss AS 7.1.1 ? Or is it better to just host app in JBoss and work backwards to fix issues one by one as suggested by some?
There is a migration center, but it says Tomcat is coming soon.
The biggest issues you would likely face are dependencies that you've included in your application that JBoss AS or WildFly already include. This is a little old, but might be helpful too.
Other than that it's tough to say what would need to be changed without knowing your environment and current configuration. The main idea behind Java EE is ideally it should work on any application server. That said, Spring isn't a Java EE standard and Tomcat is just a servlet container :) Not that there is anything wrong with either.