Using Google Drive API V3 with a Java application

on June 8, 2022

Using Google Drive API V3 with a Java application

You need to retrieve your Google Drive documents (folders and files) for your Server to Server Application ? Google Drive API v3 will help you accomplish that in a few steps. Let’s see how to easily share a Google Drive folder with your application.

1- Creation of a service account

You’ll need a service account that will interact on behalf of your application with the Google Drive API v3:

a- Create the service account on the Google Cloud Platform

go to the Service Account page
connect with the gmail account you want to retrieve the documents from
create a project
in your project, create a service account: it’s email address is generated
add a key for your service account and download it with the JSON format

b- Add access to the project for the service account

go to the IAM administration
click on “Add” at the top of the page
paste the service account email address, select the “Viewer” role and save

c- Activate the APIs

the Google Drive API here
the Cloud SQL Admin API here

d- Share the folder you want to retrieve with the service account email

Documentation : Using OAuth 2.0 for Server to Server Applications

2- Your JAVA application

a- Dependencies

In order to use the Google Drive Api v3, you’ll have to add the following dependencies in your pom.xml:

        <dependency>
            <groupId>com.google.api-client</groupId>
            <artifactId>google-api-client</artifactId>
            <version>1.31.1</version>
        </dependency>
        <dependency>
            <groupId>com.google.auth</groupId>
            <artifactId>google-auth-library-oauth2-http</artifactId>
            <version>1.3.0</version>
        </dependency>
        <dependency>
            <groupId>com.google.apis</groupId>
            <artifactId>google-api-services-drive</artifactId>
            <version>v3-rev20201130-1.31.0</version>
        </dependency>

b- Retrieving the document’s metadata

By using the Google Drive API v3, you will be able to retrieve the documents’ metadata: the file’s id, name, created time… The complete list is available here.

public class GoogleDriveApplication {
    private static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();
    private static final String CREDENTIALS_FILE_PATH = "/googleddrive-XXXXXXXXX.json";
    private static final String SERVICE_ACCOUNT = "serviceAccountName@projectName.iam.gserviceaccount.com";
    private static final String APPLICATION_NAME = "projectName";
    private static final List<String> SCOPES = Arrays.asList(DriveScopes.DRIVE);
    private static final String ROOT_FOLDER = "xxxxxxxxxxxxxxxxxx";
    private static final String projection = "files(name, id, parents, createdTime, modifiedTime, …)";
    private static Drive driveService;

    public static void main(String... args) throws IOException, GeneralSecurityException {
        buildApiService();
        List<File> files = getChildren(ROOT_FOLDER);
        ...
    }
    // CREATE THE CONNEXION TO THE API
    public static void buildApiService() throws IOException, GeneralSecurityException {
        final NetHttpTransport HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
        InputStream resourceAsStream = GoogleDriveApplication.class.getResourceAsStream(CREDENTIALS_FILE_PATH);
        HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(
        ServiceAccountCredentials.fromStream(resourceAsStream).createScoped(SCOPES).createDelegated(SERVICE_ACCOUNT));
        driveService = new Drive.Builder(HTTP_TRANSPORT, JSON_FACTORY,                       requestInitializer).setApplicationName(APPLICATION_NAME).build();
    }

    // GET THE METADATA OF THE FILES STORED IN YOUR GOOGLE DRIVE
    public static List<File> getChildren(String id) throws IOException {
        String query = "'" + id + "'" + " in parents";
        FileList directChildren = driveService.files().list().setQ(query).setFields(projection).execute();
        List<File> files = directChildren.getFiles();
        … // Here your treatment...
        return files;   
}}

c- Retrieving the file’s binary

In your Google Drive, you can store different kinds of documents: Google Drive mimetypes, Google Drive extensions (draw.io, Adobe Acrobat – PDF and e-signature tools, …) or any other mimetypes. Hereafter are precisions about the availability of the binary and the size for the most encountered mimetypes.

	Is the binary available ?	Are download/export available ?	Is the size available ?
gsheet, gdoc, gslides, gdraw	yes	yes	no
gform, gmap	no	no	no
Google Drive extensions	only some of them have	no	yes
pdf	yes	yes	yes
doc, docx	yes	yes	yes
xls, xlsx	yes	yes	yes
ppt, pptx	yes	yes	yes
jpg, jpeg, png	yes	yes	yes
odp, odt, ods	no	yes	yes
txt	no	yes	yes
xml	no	yes	yes
dcm	no	yes	yes
bin	no	yes	yes
wav, mp3, ogg, aiff	no	yes	yes
mp4	no	yes	yes

The JAVA code:

The retrieving of the binary requires a different method depending on these extensions:

public static void getOutputStream(File file, OutputStream outputStream) throws IOException {
        try {
            // YOU CAN DOWNLOAD GOOGLE DRIVE FILES IN PDF FOR EXAMPLE
            if (file.getMimeType().contains("application/vnd.google-apps.")) {
                driveService.files().export(file.getId(), "application/pdf").executeMediaAndDownloadTo(outputStream);
            // OTHER FILES ARE RETRIEVED IN THEIR ORIGINAL MIME TYPE
            } else {
                driveService.files().get(file.getId()).executeMediaAndDownloadTo(outputStream);
            }
        } catch (IOException e) {
            throw new IOException("Error getting outputStream for file:" + file + " - error: " + e);
        }
    }
}

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