Access Ad Manager storage buckets

Google provides code samples and libraries for Google Cloud Storage. The following Java example for reading a file from an Ad Manager cloud storage bucket shows how the components you've configured when setting up the service account might factor into your code:

• Project name: Name of the Google Cloud Storage project.

• Service account email address: Email address you generated.

• .p12 key file: File you downloaded.

• Bucket name: Google provides this name when you activate a feature that uses Ad Manager cloud storage buckets.

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.security.GeneralSecurityException;
import java.util.Collections;

import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.services.storage.Storage;
import com.google.api.services.storage.model.StorageObject;

public class GcsApiTest {
    /**
     * The name of the project under which the service account was created.
     * 
     * This information is displayed under the Google Developers Console.
     */
    private static final String PROJECT_NAME = "project name";

    /**
     * Developer Email address of the service account.
     * 
     * This email is generated upon creating a Service Account Client ID in your
     * Google Developers Console, and can be retrieved from the Credentials
     * page. This email must also be added to the Google Group used to control
     * access to the storage bucket.
     */
    private static final String SERVICE_ACCOUNT_EMAIL = "service account email address";

    /**
     * Bucket to use for storage operations.
     * 
     * The name of this bucket was provided to you by your Account
     * Manager. It likely has a name similar to "gdfp-12345678" or
     * "gdfp_cookieupload_12345678", depending on the Ad Manager add-on you're using.
     */
    private static final String BUCKET_NAME = "bucket name";

    /**
     * Google Cloud Storage OAuth 2.0 scope for read/write. This should
     * correspond to the access rights that your Google Group has for the
     * bucket, and you cannot request access rights that are not granted to the
     * Group (which may be read_only).
     */
    private static final String STORAGE_SCOPE = 
        "https://googleapis.com/auth/devstorage.read_write";

    /**
     * Path to the key.p12 file providing access to the bucket.
     * 
     * This file is created when the service client ID is created. If you don't
     * have this file, you will need to generate a new client p12 key from the
     * Google Developers Console.
     */
    private static final String KEY_P12 = "path to .p12 key file";

    /** HTTP transport. */
    private HttpTransport httpTransport;
    private Storage storage;

    // constructor, sets up credentials and storage objects
    public GcsApiTest() {
	File p12File = new File(KEY_P12);

	try {
	    httpTransport = GoogleNetHttpTransport.newTrustedTransport();

	    GoogleCredential credential = new GoogleCredential.Builder()
		    .setTransport(httpTransport)
		    .setJsonFactory(JacksonFactory.getDefaultInstance())
		    .setServiceAccountId(SERVICE_ACCOUNT_EMAIL)
		    .setServiceAccountScopes(
			    Collections.singleton(STORAGE_SCOPE))
		    .setServiceAccountPrivateKeyFromP12File(p12File).build();
	    storage = new Storage.Builder(httpTransport,
		    JacksonFactory.getDefaultInstance(), credential)
		    .setApplicationName(PROJECT_NAME).build();
	} catch (GeneralSecurityException | IOException e1) {
	    e1.printStackTrace();
	    System.exit(1);
	}
    }

    /**
     * Method to return the name of the first file in the bucket.
     * 
     * @return the name of the file, or null if the bucket is empty
     * @throws IOException
     */
    public String GetFirstFile() throws IOException {
	Storage.Objects.List listObjects = storage.objects().list(BUCKET_NAME);
	listObjects.setMaxResults(5L);
	com.google.api.services.storage.model.Objects objects = listObjects
		.execute();

	// empty bucket?
	if (null == objects.getItems() || objects.getItems().isEmpty()) {
	    System.out.println("Bucket \"" + BUCKET_NAME
		    + "\" empty or invalid.");
	    return null;
	}

	StorageObject object = objects.getItems().get(0);
	System.out.println("First object in bucket: \"" + object.getName()
		+ "\".");
	return object.getName();
    }

    /**
     * Method to download the specified file from the storage bucket
     * 
     * @param filename
     *            Name of the file that should be downloaded.
     * @throws IOException
     */
    public void DownloadFile(String filename) throws IOException {
	Storage.Objects.Get getObject = storage.objects().get(BUCKET_NAME,
		filename);
	OutputStream os = new FileOutputStream(filename, true);
	getObject.getMediaHttpDownloader().setDirectDownloadEnabled(true);
	getObject.executeMediaAndDownloadTo(os);

	System.out.println("File \"" + filename + "\" downloaded.");
    }

    /**
     * Main method to execute the different tests.
     * 
     * @param args
     */
    public static void main(String[] args) {
	GcsApiTest gcsApiTest = new GcsApiTest();

	try {
	    String filename = gcsApiTest.GetFirstFile();
	    gcsApiTest.DownloadFile(filename);
	} catch (IOException e) {
	    System.out.println(e.getMessage());
	}
    }
}