Java based workflow engine required

I am looking for a java based workflow engine which is powerful enough to have most of the workflow features but simple to implement.

Features like transition from one state to another based on approvals by people who have permission to approve a state, the transition could be automatic also if all the required fields/data are available, single person or multiple person to approve a state, visual editor to create the workflow, the transition can only happen if certain fields have particular values (like rules), sending notification to approver and once approved send notification t开发者_JAVA百科o people watching the state.

It sounds like an implementation of the Business Process Execution Language (BPEL) is what you want.

To add to Samuel's suggestion, I'd suggest having a look at the videos on the OpenESB website. The NetBeans plugin is quite powerful.

More generically, see also Wikipedia's Comparison of BPEL engines.

Edit: I've also spent some time over the past week or so using Bonita Open Solution (GPLv2). In my opinion, it's superior to jBPM and Activiti. The range of plugins (i.e. business logic or notifications that you can farm off to third parties) is very impressive and the GUI editor is pretty easy to use. Furthermore, it comes out of the box with a pretty easy to use portal feature which means you can quite quickly to mockups of proper workflow tasks, assignments, etc. within a web portal. My only criticism at the moment is that I wish they'd make a more user-friendly way to connect to Web Services (it can still be done, it's just a bit fiddly). Also, the forums are actively staffed and questions usually get answered by their employees within a day.

Activity (http://activiti.org/) is the new jBPM offspring. Looks promising and if you now start with workflow, I would go for it.

How about JBoss BPM