I believe the the given example is old and corresponds to JBPM4 .
For JBPM5 there are work item handlers for Human Task and would be a nice point to start
Eg : Human task Handler using MINA interfaces
https://github.com/droolsjbpm/jbpm/blob/master/jbpm-human-task/jbpm-human-task-mina/src/main/java/org/jbpm/process/workitem/wsht/WSHumanTaskHandler.java