code: public HttpSessionActivity getHttpSessionActivity(HttpSession httpSession)
  			throws NullPointerException, IllegalArgumentException, IllegalStateException,
  			ActivityAlreadyExistsException, StartActivityException,
  			SLEEException {
  		if (httpSession == null) {
  			throw new NullPointerException("null http session");
  		}
  		if (!(httpSession instanceof HttpSessionWrapper)) {
  			throw new IllegalArgumentException();
  		}
  		final HttpSessionWrapper httpSessionWrapper = (HttpSessionWrapper) httpSession;
  		final HttpSessionActivityImpl activity = new HttpSessionActivityImpl(httpSessionWrapper);
  		if (httpSessionWrapper.getResourceEntryPoint() == null) {
  			ra.getSleeEndpoint().startActivitySuspended(activity,activity);
  			httpSessionWrapper.setResourceEntryPoint(ra.getName());
  		}
  		return activity;
  	}
docs: /*
  (non-Javadoc)
  @see net.java.slee.resource.http.HttpServletRaSbbInterface#getHttpSessionActivity(javax.servlet.http.HttpSession)