Hi Tun,
You have to cast execution to ExecutionImpl. Then get the current activity of this execution. Something like this:
ExecutionImpl executionImpl = (ExecutionImpl) execution;
Activity activity = executionImpl.getActivity();
List<? extends Transition> incomingTransitions = activity.getIncomingTransitions();
for (Transition transition : incomingTransitions) {
Activity incomingActivity = transition.getSource();
// here is the name of incomging activity
}