code: public synchronized GoogleCalendarService getCalendarService(String accountId) throws IOException {
          if (calendarService == null) {
              Credential credential = impl_getStoredCredential(accountId);
              if (credential == null) {
                  throw new UnsupportedOperationException("The account has not been authorized yet!");
              }
              calendarService = new GoogleCalendarService(impl_createService(credential));
          }
          return calendarService;
      }
docs: Instances a new calendar service for the given google account user name.
  This requires previous authorization to get the service, so if the user
  has not granted access to his data, this method will start the
  authorization process automatically; this attempts to open the login google page in the
  default browser.
  
  @param accountId
  The google account.
  @return The calendar service, this can be null if the account cannot be
  authenticated.
  @throws IOException If the account has not been authenticated.