We currently have an application that is based on an in-house developed workflow engine with YAML based DSL. We are looking to move parts of it to Java.

I have discovered a number of java solutions like Intalio, JBPM, Drools Expert, Drools Flow etc. They appear to be aimed at businesses where the business analyst creates the workflows using a graphical editor and submits them to the workflow engine. They seem geared towards ease of use for non-technical people rather than for developers with a focus on human interaction.

The workflows tend to look like.

Discover-a-file        -\
                         -> join -> process-file -> move-file -> register-file 
Discover-some-metadata -/

If any step fails we need to retry it X times. We also need to be able to stop the system and be able to restart it and have it continue from where it was (durable).

Some of our workflows can be defined by a set of goals we need to achieve so Jess's backwards rule chaining sounds interesting but it is not open source.

It might be that what we are after is a Finite State Machine engine or just an Enterprise Service Bus and do everything as JMS queues.

Is there a good open source workflow engine that is both standards-based but also geared towards developers. We don't particular want to use a graphical workflow designer or write reams of XML and it should ideally be in Java or language agnostic (makes REST/Soap calls to external services).

Thanks, Tom