code: public static Credential getServiceAccountCredential(String serviceAccountId,
        String privateKeyFile) throws GeneralSecurityException, IOException {
      return getServiceAccountCredential(serviceAccountId, privateKeyFile, DatastoreOptions.SCOPES);
    }
docs: Constructs credentials for the given account and key.
  
  @param serviceAccountId service account ID (typically an e-mail address).
  @param privateKeyFile the file name from which to get the private key.
  @return valid credentials or {@code null}