when i try to list gmail threads using Gmail API i get GoogleJsonResponseException: 500 Internal Server Error

Question

I am trying to use GMAIL API to download attachments from my email account using OAuth 2.0 server to server Application. Here is my code:

    private static final String USER = "[email protected]";
    private static String emailAddress = "[email protected]";
    {
       try {
              httpTransport = GoogleNetHttpTransport.newTrustedTransport();
              credential = new GoogleCredential.Builder()
              .setTransport(httpTransport)
              .setJsonFactory(JSON_FACTORY)
              .setServiceAccountId(emailAddress)
              .setServiceAccountPrivateKeyFromP12File(new File("myfile.p12"))
              .setServiceAccountScopes(Collections.singleton(GmailScopes.GMAIL_READONLY))
              .build();
          }
          catch (IOException | GeneralSecurityException e)
          {
              throw new RuntimeException(e);
          }
    }
    // Create a new authorized Gmail API client
    Gmail service = new Gmail.Builder(httpTransport, JSON_FACTORY, credential)
        .setApplicationName(APP_NAME).build();

    // Retrieve a page of Threads
    ListThreadsResponse threadsResponse = service.users().threads().list(USER).execute();
      List<Thread> threads = threadsResponse.getThreads();

   // Print ID of each Thread.
    for (Thread thread : threads) {
      System.out.println("Thread ID: " + thread.getId());

}

I get the error at the threadsResponse call. These are the errors:

Exception in thread "main" com.google.api.client.googleapis.json.GoogleJsonResponseException: 500 Internal Server Error.

{ "code" : 500, "errors" : [ { "domain" : "global", "message" : "Backend Error", "reason" : "backendError" } ], "message" : "Backend Error" } at com.google.api.client.googleapis.json.GoogleJsonResponseException.from(GoogleJsonResponseException.java:145) at com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(AbstractGoogleJsonClientRequest.java:113) at com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(AbstractGoogleJsonClientRequest.java:40) at com.google.api.client.googleapis.services.AbstractGoogleClientRequest$1.interceptResponse(AbstractGoogleClientRequest.java:312) at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:1049) at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:410) at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:343) at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.execute(AbstractGoogleClientRequest.java:460) at core.crescent.gmail.GmailApiQuickstart.main(GmailApiQuickstart.java:192)

If you want to access a single user, you can use authentication for single user instead of service account. I don't think gmail API supports service account. stackoverflow.com/questions/24523003/… — SGC
– SGC, Commented Jan 5, 2015 at 22:39
I am using OAuth2 Server to server application link because it seems like it's the only way to get authorization to access a gmail account without a user consent (without having to open browsers and do manual consent). Is there another way to accomplish this. Thank you — HBizzle
– HBizzle, Commented Jan 12, 2015 at 19:06

Matthias Berth · Accepted Answer · 2015-01-07 16:22:55Z

0

You could retry the request, with exponential backoff. Worked for me. See https://developers.google.com/drive/web/handle-errors

answered Jan 7, 2015 at 16:22

Matthias Berth

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HBizzle · Accepted Answer · 2015-01-13 19:29:01Z

0

So I figured out the issue and fixed it!

When setting up "Credential" (in the code I posted above). I needed to add .setServiceAccountUser(USER) sub-routine. By doing this, you make the link between the service account created and the GMAIL account you want to access. I saw it earlier in https://developers.google.com/accounts/docs/OAuth2ServiceAccount, but I was under the impression that it was only if you wanted to link with an account under a different domain name.

This fixed my issues. Thank you all for your responses

answered Jan 13, 2015 at 19:29

HBizzle

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