I would advice against using entry/exit action of a human task to store code, it can be a nightmare to figure out where did you place code since there is no visual clue when a human task has code.
You could try a script task or, as core developers recommend, you can use a custom WorkitemHandler. The latter will help in separation of code from the bpmn2 file and a custom service task will be easier to reuse in other processes instead of copy/paste. You can find the documentation here (jBPM 6) http://docs.jboss.org/jbpm/v6.0.1/userguide/jBPMDomainSpecificProcesses.html