部署时无法从google云存储上传和下载文件

Question

public class DataStorageTestServlet extends HttpServlet {
    private final GcsService gcsService = GcsServiceFactory.createGcsService(RetryParams.getDefaultInstance());
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws IOException {
        resp.setContentType("text/plain");
        byte[] file = {1, 2, 3, 4, 5, 6};
        GcsFilename fileName = new GcsFilename("charlie-first-bucket", "a");
        writeToFile(fileName, file);
        resp.getWriter().println(readFromFile(fileName));
    }