Someone posted a sample app in the GWT Console that uses Spring MVC and BPM Console Server's REST API. I've had some troubles getting it running against my Console Server instance but maybe you will find it an interesting example.
https://community.jboss.org/message/725143#725143
It's worth noting the Spring MVC app in the example above doesn't hit jBPM directly, rather it makes REST calls to the Console Server which surfaces a REST API. Myself I'm wondering if it is preferrable to use this approach or to have my web application integrate directly with jBPM API. I've posted a discussion on that topic here.
https://community.jboss.org/thread/199537?tstart=0