Thanks for the reply. I was primarily attracted to spring-drools because of the use of Java to define complex logic in the conditions, but I have since found this old thread that summarizes pretty nicely how to do that without spring-drools:
Based on the above suggestion of using "facts" I've come up with the following rule:
rule "Decline Request" dialect "mvel" when request : Request( status == ( RequestStatus.validated ) ) Condition( request == request, failed == "true" )
then request.setStatus( requestStatus.declined ); update( request ); end
Then I insert into the session Java classes that extend my Condition abstract. Each Condition contains the request, and should any Condition return true from its getFailed method, then the request is declined.