code: public static DownloadResponse downloadFile(Drive drive, String fileId) throws IOException {
  	  Get request = drive.files().get(fileId).setAlt("media");
  	  String contentType = request.executeUsingHead().getContentType();
  	  if (StringUtils.isNotBlank(contentType)) {
    	  try (InputStream inputStream = request.executeAsInputStream()) {
  	      return new DownloadResponse(contentType, IOUtils.toByteArray(inputStream));
        }
  	  }
  	  
  	  return null;
  	}
docs: Downloads file from Google Drive
  
  @param drive drive client
  @param fileId file id for file to be downloaded
  @return file content
  @throws IOException an IOException