GoogleCredential Missing Access Token

Question

I am using the service account model and Google's Java API to retrieve and modify users.

I am able to successfully create a GoogleCredential object using code similar to Google's example:

GoogleCredential googleCredential = new GoogleCredentialBuilder()
    .setTransport(httpTransport)
    .setJsonFactory(jsonFactory)
    .setServiceAccountId(SERVICE_ACCOUNT_EMAIL)
    .setServiceAccountUser(SERVICE_ACCOUNT_USER)
    .setServiceAccountPrivateKeyFromP12File(P12_PRIVATE_KEY_FILE)
    .setServiceAccountScopes(Collections.singleton(GLOBAL_USER_AND_ALIAS_SCOPE)
    .build();

I see no mention in any examples that I have to explicitly create an access token, so I have been assuming that the above code takes care of that. Is that true?

After that, I successfully create an instance of Directory, then try to retrieve a specific user:

User user = new User();
user = directory.users().get(uid).execute();

That fails, throwing a NullPointerException.

When I inspect the GoogleCredential object right before the call to get the user object, it appears that it does not contain an access token:

accessToken = null
refreshToken = null

What am I missing?

How does one get the access token using the service account model?

Thanks in advance.

Answer 1

Where are you getting your accessToken? Try

credential.refreshToken();
accessToken = credential.getAccessToken();

Also, you should consider running your credentials in the Oauth2 Playground . If it works in the playground, then it's likely something wrong with your implementation.

Answer 2

Andy is correct. The examples for the Google Java API leave out this critical step. At runtime, the Google code throws a NullPointerException with no other details that would identify where it is occurring. Stepping through the debugger in Eclipse made it clear that the token was null in GoogleCredential.