Dude, you are responsible for showing the web form, the jBPM4 API can't read your mind and doesn't know what view technologie you are using.
All the jBPM4 API can do for you is give you a String/URL:
RepositoryService.getStartFormResourceName(String processDefinitionId, String activityName);
or
Task.getFormResourceName();
but you have to do the rest by creating and showing the view to the user.