从 App Engine Endpoints 访问 Google API (Java)

Question

I would like to make calls to the Google Calendar API App Engine Java Endpoints. This is my (incomplete) utility class for calling the Google Calendar. I am trying to retrieve or create the User's Google Calendar specific to my App 'Zeppa' from an authenticated endpoint. I do this by calling zeppaCalendarEntry(User) where user is the user instance from the authenticated call. The API console has the Calendar API on and the client_secrets.json file is for App Engine and Service Accounts.

The error occurs in Get Client Credential, a null InputStream is returned. Any references to standard procedure or fixes would be great.

class ZeppaCalendarUtils {



private ZeppaCalendarUtils() {
    }

    /**
     * Global instance of the {@link DataStoreFactory}. The best practice is to
     * make it a single globally shared instance across your application.
     */
    private static final AppEngineDataStoreFactory DATA_STORE_FACTORY = AppEngineDataStoreFactory
            .getDefaultInstance();

    /** Global instance of the HTTP transport. */
    static final HttpTransport HTTP_TRANSPORT = new UrlFetchTransport();

    /** Global instance of the JSON factory. */
    static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();

    private static GoogleClientSecrets clientSecrets = null;

    /**
     * Creates a new Google Calendar for user
     * @param calendarClient
     * @return
     * @throws GeneralSecurityException
     * @throws IOException
     */
    private static CalendarListEntry createZeppaCalendarEntry(
            Calendar calendarClient) throws GeneralSecurityException,
            IOException {

        CalendarListEntry content = new CalendarListEntry();
        content.setAccessRole(Constants.CALENDAR_ACCESS_ROLE);
        content.setBackgroundColor(Constants.CALENDAR_COLOR_BACKGROUND);
        content.setForegroundColor(Constants.CALENDAR_COLOR_FOREGROUND);
        content.setDefaultReminders(Constants.CALENDAR_DEFAULT_REMINDERS);
        content.setSelected(Constants.CALENDAR_SELECTED);
        content.setSummary("Zeppa");
        content.setId(Constants.CALENDAR_ID);

        CalendarListEntry result = calendarClient.calendarList()
                .insert(content).execute();

        return result;

    }

    /**
     * Retrieve or create a Users calendar
     * @param user
     * @return
     * @throws GeneralSecurityException
     * @throws IOException
     */
    public static CalendarListEntry zeppaCalendarEntry(User user)
            throws GeneralSecurityException, IOException {

        Calendar calendarClient = loadCalendarClient(user.getUserId());
        CalendarListEntry result = calendarClient.calendarList()
                .get(Constants.CALENDAR_ID).execute();

        if (result == null) {
            result = createZeppaCalendarEntry(calendarClient);
        }

        return result;
    }

    /**
     * Retrieve a Client Secrets
     * @return
     * @throws IOException
     */
    static GoogleClientSecrets getClientCredential() throws IOException {
        if (clientSecrets == null) {

            InputStream stream = ZeppaCalendarUtils.class
                    .getResourceAsStream("client_secrets.json");

            Reader clientSecretReader = new InputStreamReader(stream);
            clientSecrets = GoogleClientSecrets.load(JSON_FACTORY,
                    clientSecretReader);
        }
        return clientSecrets;
    }

    /**
     * Generate the calendar client for calls to the API
     * @param userId
     * @return
     * @throws IOException
     */
    private static Calendar loadCalendarClient(String userId)
            throws IOException {
        Credential credential = newAuthFlow().loadCredential(userId);
        return new Calendar.Builder(HTTP_TRANSPORT, JSON_FACTORY, credential)
                .build();
    }


    /**
     * Create an auth flow
     * @return
     * @throws IOException
     */
    private static GoogleAuthorizationCodeFlow newAuthFlow() throws IOException {
        return new GoogleAuthorizationCodeFlow.Builder(HTTP_TRANSPORT,
                JSON_FACTORY, getClientCredential(),
                Collections.singleton(CalendarScopes.CALENDAR))
                .setDataStoreFactory(DATA_STORE_FACTORY)
                .setAccessType("offline").build();
    }

}

Answer 1

If you check the docs recommended method to connect to a Google API from App Engine, you can see that it doesn't use the classloader's getResourceAsStream , it uses a FileInputStream on a File object. Try to use that instead and see if it stops returning null.