private static void initProvider(final Class<? extends VCardProvider> clazz) {
        try {
            provider = clazz.newInstance();
        }
        catch (Exception e) {
            Log.error("Error loading vcard provider: " + clazz.getName(), e);
            provider = new DefaultVCardProvider();
        }
    }
Returns the vCard of a given user or null if none was defined before. Changes to the
returned vCard will not be stored in the database. Use the returned vCard as a
read-only vCard.

@param username Username (not full JID) whose vCard to retrieve.
@return the vCard of a given user.
xmppserver/src/main/java/org/jivesoftware/openfire/vcard/VCardManager.java