Google Drive access

Question

I tried to run this Java code in order to list all files in my Google Drive:

import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.extensions.java6.auth.oauth2.AuthorizationCodeInstalledApp;
import com.google.api.client.extensions.jetty.auth.oauth2.LocalServerReceiver;
import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeFlow;
import com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets;
import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.client.util.store.FileDataStoreFactory;
import com.google.api.services.drive.Drive;
import com.google.api.services.drive.DriveScopes;
import com.google.api.services.drive.model.*;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.List;

public class Quickstart
{
    /**
     * Application name.
     */
    private static final String APPLICATION_NAME = "Drive API Java Quickstart";

    /**
     * Directory to store user credentials for this application.
     */
    private static final java.io.File DATA_STORE_DIR = new java.io.File(
        System.getProperty("user.home"), ".credentials/drive-java-quickstart");

    /**
     * Global instance of the {@link FileDataStoreFactory}.
     */
    private static FileDataStoreFactory DATA_STORE_FACTORY;

    /**
     * Global instance of the JSON factory.
     */
    private static final JsonFactory JSON_FACTORY
        = JacksonFactory.getDefaultInstance();

    /**
     * Global instance of the HTTP transport.
     */
    private static HttpTransport HTTP_TRANSPORT;

    /**
     * Global instance of the scopes required by this quickstart.
     *
     * If modifying these scopes, delete your previously saved credentials at ~/.credentials/drive-java-quickstart
     */
    private static final List<String> SCOPES = Arrays.asList(DriveScopes.DRIVE_METADATA_READONLY);

    static
    {
        try
        {
            HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
            DATA_STORE_FACTORY = new FileDataStoreFactory(DATA_STORE_DIR);
        }
        catch (Throwable t)
        {
            t.printStackTrace();
            System.exit(1);
        }
    }

    /**
     * Creates an authorized Credential object.
     *
     * @return an authorized Credential object.
     * @throws IOException
     */
    public static Credential authorize() throws IOException
    {
        // Load client secrets.
        InputStream in
            = Quickstart.class.getResourceAsStream("/development-241a19899242.json");
        GoogleClientSecrets clientSecrets
            = GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(in));

        // Build flow and trigger user authorization request.
        GoogleAuthorizationCodeFlow flow
            = new GoogleAuthorizationCodeFlow.Builder(
                HTTP_TRANSPORT, JSON_FACTORY, clientSecrets, SCOPES)
            .setDataStoreFactory(DATA_STORE_FACTORY)
            .setAccessType("offline")
            .build();
        Credential credential = new AuthorizationCodeInstalledApp(
            flow, new LocalServerReceiver()).authorize("user");
        System.out.println(
            "Credentials saved to " + DATA_STORE_DIR.getAbsolutePath());
        return credential;
    }

    /**
     * Build and return an authorized Drive client service.
     *
     * @return an authorized Drive client service
     * @throws IOException
     */
    public static Drive getDriveService() throws IOException
    {
        Credential credential = authorize();
        return new Drive.Builder(
            HTTP_TRANSPORT, JSON_FACTORY, credential)
            .setApplicationName(APPLICATION_NAME)
            .build();
    }

    public static void main(String[] args) throws IOException
    {
        // Build a new authorized API client service.
        Drive service = getDriveService();

        // Print the names and IDs for up to 10 files.
        FileList result = service.files().list()
            .setPageSize(10)
            .setFields("nextPageToken, files(id, name)")
            .execute();
        List<File> files = result.getFiles();
        if (files == null || files.size() == 0)
        {
            System.out.println("No files found.");
        }
        else
        {
            System.out.println("Files:");
            for (File file : files)
            {
                System.out.printf("%s (%s)\n", file.getName(), file.getId());
            }
        }
    }
}

When I run the code I'm redirected to login page to enter my Google's e-mail credentials. How I can skip this step? The code I will entirely in background I need to use the credentials in a JSON file.

Answer 1

You might want to check using a service account and Perform Google Apps Domain-Wide Delegation of Authority.

In enterprise applications you may want to programmatically access users data without any manual authorization on their part. In Google Apps domains, the domain administrator can grant to third party applications domain-wide access to its users' data — this is referred as domain-wide delegation of authority. To delegate authority this way, domain administrators can use service accounts with OAuth 2.0.

Here is the link for creating a service account:

Authorizing a service account to access data on behalf of users in a domain is sometimes referred to as "delegating domain-wide authority" to a service account.

And if you have delegated domain-wide access to the service account and you want to impersonate a user account, specify the email address of the user account with the setServiceAccountUser method of the GoogleCredential factory. For example:

GoogleCredential credential = new GoogleCredential.Builder()
    .setTransport(httpTransport)
    .setJsonFactory(JSON_FACTORY)
    .setServiceAccountId(emailAddress)
    .setServiceAccountPrivateKeyFromP12File(new File("MyProject.p12"))
    .setServiceAccountScopes(Collections.singleton(SQLAdminScopes.SQLSERVICE_ADMIN))
    .setServiceAccountUser("user@example.com")
    .build();

There is also a tutorial about Google Drive API with a Service Account, it is not in Java but I hope this helps you understand how to use Google Drive and service account.

Do you want to upload to an account that you personally have control of? You don’t need the users to authenticate themselves with Google. What you need to use is the Google Drive API with a service account.

Hope this helps.