@Override
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
resp.setContentType("text/plain");
Student student = AuthController.getCurrentStudent();
Objectify ofy = Registry.dao().ofy();
resp.getWriter().println("Cleaning activities...");
QueryResultIterable<Key<Activity>> activities = ofy.query(Activity.class).filter("student =", student).fetchKeys();
ofy.delete(activities);