How to inject spring beans from external war?

I'd like to create a decoupled frontend (vaadin) and backend (spring). Both should run on the same tomcat application server, but each is a single war so I can redeploy the frontend without having to restart the backend.

I want to minimize the remoting code between both applications to exchange data. Therefore I thought I could maybe inject the service beans from backend into the frontend war. But it that possible? How would I share the service declaration between both war files / java projects?

And what type of remoting would be apropriate here? Ideally I could imagine to have a mechanism where I could just "use" the backend service classes also in frontend, and spring clues the proxies together. But how?