I recommend  you have a look at the following web-site which introduces tens of open source workflow  managements and business process managements, all written in java and J2EE.

java-source.net/open-source/workflow-engines

I did the same survey for my company and we chose Enhydra Shark workflow engine  for our project. You may need to survey this workflow and study its documentations. All you need to know before hiring it in your project, are here:

http://shark.objectweb.org/