After I googled it, I found the recommended way to do this is creating Custom Workitem Handler in JBPM.
I already followed step-by-step instruction from this web : http://fxapps.blogspot.co.id/2015/04/creating-custom-work-item-handler-in.html
But when I want to save my Business Process, it show "Error Storing Asset : 0". And I can not find any error message that show the exactly what is wrong.
So for this moment I stuck.
Can anyone help me to solve this issue?
Very appreciate for your help.