I've successfully installed and run the [Google Drive Quick Start application called DriveCommandLine](https://developers.google.com/drive/quickstart). I've also adapted it a little to GET file info for one of the files in my Drive account.

What I would like to do now is save the credentials somehow and re-use them without the user having to visit a web page each time to get an authorization code. I have checked out [this page](https://developers.google.com/accounts/docs/OAuth2) with instructions to Retrieve and Use OAuth 2.0 credentials. In order to use the example class (MyClass), I have modified the line in DriveCommandLine where the Credential object is instantiated:

```
Credential credential = MyClass.getCredentials(code, "");

```

This results in the following exception being thrown:

```
java.lang.NullPointerException
    at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:187)
    at com.google.api.client.json.jackson.JacksonFactory.createJsonParser(JacksonFactory.java:84)
    at com.google.api.client.json.JsonFactory.fromInputStream(JsonFactory.java:247)
    at com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets.load(GoogleClientSecrets.java:168)
    at googledrive.MyClass.getFlow(MyClass.java:145)
    at googledrive.MyClass.exchangeCode(MyClass.java:166)
    at googledrive.MyClass.getCredentials(MyClass.java:239)
    at googledrive.DriveCommandLine.<init>(DriveCommandLine.java:56)
    at googledrive.DriveCommandLine.main(DriveCommandLine.java:115)

```

I've been looking at these APIs (Google Drive and OAuth) for 2 days now and have made very little progress. I'd really appreciate some help with the above error and the problem of getting persistent credentials in general. 

This whole structure seems unnecessarily complicated to me. Anybody care to explain why I can't just create a simple Credential object by passing in my Google username and password?

Thanks,
Brian O Carroll, Dublin, Ireland

**\* Update \***

Ok, I've just gotten around the above error and now I have a new one.

The way I got around the first problem was by modifying MyClass.getFlow(). Instead of creating a GoogleClientServices object from a json file, I have used a different version of GoogleAuthorizationCodeFlow.Builder that allows you to enter the client ID and client secret directly as Strings:

```
flow = new GoogleAuthorizationCodeFlow.Builder(httpTransport, jsonFactory, "<MY CLIENT ID>", "<MY CLIENT SECRET>", SCOPES).setAccessType("offline").setApprovalPrompt("force").build();

```

The problem I have now is that I get the following error when I try to use flow (GoogleAuthorizationCodeFlow object) to exchange the authorization code for the Credentials object:

```
An error occurred: com.google.api.client.auth.oauth2.TokenResponseException: 400 Bad Request
{
  "error" : "invalid_scope"
}
googledrive.MyClass$CodeExchangeException
        at googledrive.MyClass.exchangeCode(MyClass.java:185)
        at googledrive.MyClass.getCredentials(MyClass.java:262)
        at googledrive.DriveCommandLine.<init>(DriveCommandLine.java:56)
        at googledrive.DriveCommandLine.main(DriveCommandLine.java:115)

```

Is there some other scope I should be using for this? I am currently using the array of scopes provided with MyClass:

```
private static final List<String> SCOPES = Arrays.asList(
        "https://www.googleapis.com/auth/drive.file",
        "https://www.googleapis.com/auth/userinfo.email",
        "https://www.googleapis.com/auth/userinfo.profile");

```

Thanks!