Java Google Drive API在尝试获取授权令牌时返回401

我正在尝试使用oauth2.0授权对google帐户进行身份验证。我已经成功地创建了ClientID和Client Secret。重定向URI是正确的。我用于身份验证的代码是：

@Override
public void filter(HttpServletRequest request, HttpServletResponse response)
        throws Exception {
    String action = request.getParameter("action");
    if ("oauth_callback".equals(action)) {
        String providerId = request.getParameter("providerId");
        String accountId = request.getParameter("state");
        if (this.getAccount().getProvider().getId().equals(providerId)
                && this.getAccount().getId().equals(accountId)) {

            String proxyHost = System.getProperty("https.proxyHost");
            String proxyPort = System.getProperty("https.proxyPort");
            Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress(
                    proxyHost, Integer.parseInt(proxyPort)));
            HttpTransport httpTransport = new NetHttpTransport.Builder()
                    .setProxy(proxy).build();
            JsonFactory jsonFactory = new JacksonFactory();
            GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(
                    httpTransport, jsonFactory, GoogleDriveUtils.CLIENT_ID,
                    GoogleDriveUtils.CLIENT_SECRET,
                    Arrays.asList(DriveScopes.DRIVE))
                    .setAccessType("online").setApprovalPrompt("auto")
                    .build();
            String codeAttr = request.getParameter("code");
            URL serverUrl = new URL(request
                    .getRequestURL().toString());
            String host = serverUrl.getHost();
            if (serverUrl.getPort() != -1) {
                host += ":" + serverUrl.getPort();
            }
            String redirectUrl = String.format(
                    GoogleDriveUtils.REDIRECT_URL, serverUrl.getProtocol(),
                    host);
            GoogleTokenResponse googleResponse = flow
                    .newTokenRequest(codeAttr).setRedirectUri(redirectUrl)
                    .execute();
            GoogleCredential credential = new GoogleCredential()
                    .setFromTokenResponse(googleResponse);

            // Create a new authorized API client
            this.service = new Drive.Builder(httpTransport, jsonFactory,
                    credential).build();
            this.isLoggedIn = true;
            logger.debug("Authentication successful.");

            initProps();
            logger.debug("Account information initialized successfully.");

            response.sendRedirect(request.getSession().getServletContext().getContextPath());
        }
    }
}

执行此代码时：

            GoogleTokenResponse googleResponse = flow
                    .newTokenRequest(codeAttr).setRedirectUri(redirectUrl)
                    .execute();

google api返回过期的授权令牌和状态代码401。我怎样才能解决这个问题