Lots of thanks, Josh!
Your comments are very valuable.
It's just an API with libraries that implement support for connecting to, and sending and receiving events from, external systems.
So it can be used to integrate external systems, no matter what framework is used on these external systems, therefore Spring Integration is not only addressed to applications / systems built using the Spring framework, you can use Spring integration to integrate any kind of external systems. That's very good! (I supossed it has to be this way to guarantee its successfulness, but you never know for sure what policies rule over a project). I agree with your recommendations about learning and using Spring Integration. Green Beans already added in my bookmarks list. Thanks again.