HttpTransport httpTransport = new NetHttpTransport();
JsonFactory jsonFactory = new JacksonFactory();
AppIdentityCredential credential =
   new AppIdentityCredential.Builder(Arrays.asList(DriveScopes.DRIVE)).build();
// API_KEY is from the Google Console as a server API key
GoogleClientRequestInitializer keyInitializer =
   new CommonGoogleClientRequestInitializer("<my-service-account-key>");
Drive service = new Drive.Builder(httpTransport, jsonFactory, null)
   .setHttpRequestInitializer(credential)
   .setGoogleClientRequestInitializer(keyInitializer)
   .setApplicationName("<my-service-account-name>").build();

String pageToken = null;
do {
   StringBuilder query = new StringBuilder(
                "'" + folderId + "' in parents and mimeType != 'application/vnd.google-apps.folder' and trashed = false");
   FileList result = service.files().list()
      .setQ(query.toString())
      .setSpaces("drive")
      .setFields("nextPageToken, files(id, name)")
      .setPageToken(pageToken).execute();
   // do something
} while (pageToken != null);