How can I run google apps script deployed as web app from Java servlet?

Question

I created a GAS and deployed it as google web app. it is available with https://script.google.com/macros/s/..../exec URL. Now I want to run it from Java servlet. I created application in console.developers.google.com, created CLIENT ID for Service account and API KEY and private key file.

Now I'm trying to run script as follows:

    HttpTransport httpTransport = GoogleNetHttpTransport.newTrustedTransport();
    JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();
    // Build service account credential.
    GoogleCredential credential = new GoogleCredential.Builder().setTransport(httpTransport)
        .setJsonFactory(jsonFactory)
        .setServiceAccountId("[email protected]")
        .setServiceAccountScopes(Collections.singleton("https://script.google.com"))
        .setServiceAccountPrivateKeyFromP12File(new File(getClass().getClassLoader().getResource("key/eForms-055a7029cd36.p12").toURI()).getAbsoluteFile())
        .build();

            // Set up and execute a Google Cloud Storage request.
    String URI = "https://script.google.com/macros/s/.../exec?payload="+form.toString();
    HttpRequestFactory requestFactory = httpTransport.createRequestFactory(credential);
    GenericUrl url = new GenericUrl(URI);
    HttpRequest http_request = requestFactory.buildGetRequest(url);
    HttpResponse response = http_request.execute();
    String content = response.parseAsString();

And I get

com.google.api.client.auth.oauth2.TokenResponseException: 400 Bad Request
{
  "error" : "invalid_grant"
}

I think that I set wrong slot, but which one to set?