If you want get taskform of started process.
There is code gwt-console & gwt-concole-server https://github.com/bpmc/bpm-console
Look at file FormProcessingFacade.java in project gwt-console-server-war-base. (https://github.com/bpmc/bpm-console/blob/master/server/war-base/src/main/java/org/jboss/bpm/console/server/FormProcessingFacade.java).
See also Resteasy2.3.X (http://www.jboss.org/resteasy/docs.html).
You can change server code and change request like this http://localhost:8080/jbpm-console/whatever/{workflowId}/{taskId}.
Sorry for my poor english