restygwt/src/main/java/org/fusesource/restygwt/client/callback/CachingCallbackFilter.java
protected String[] getCacheDomains(Method method) {
        if (null == method.getData().get(Domain.CACHE_DOMAIN_KEY)) {
            return null;
        }

        JSONValue jsonValue = JSONParser.parseStrict(method.getData().get(Domain.CACHE_DOMAIN_KEY));
        if (null == jsonValue) {
            return null;
        }

        JSONArray jsonArray = jsonValue.isArray();
        if (null != jsonArray) {
            String[] dd = new String[jsonArray.size()];
            for (int i = 0; i < jsonArray.size(); ++i) {
                dd[i] = jsonArray.get(i).isString().stringValue();
            }

            return dd;
        }
        return null;
    }
protected String[] getCacheDomains(Method method) {
        if (null == method.getData().get(Domain.CACHE_DOMAIN_KEY)) {
            return null;
        }

        JSONValue jsonValue = JSONParser.parseStrict(method.getData().get(Domain.CACHE_DOMAIN_KEY));
        if (null == jsonValue) {
            return null;
        }

        JSONArray jsonArray = jsonValue.isArray();
        if (null != jsonArray) {
            String[] dd = new String[jsonArray.size()];
            for (int i = 0; i < jsonArray.size(); ++i) {
                dd[i] = jsonArray.get(i).isString().stringValue();
            }

            return dd;
        }
        return null;
    }
when using the {@link Domain} annotation on services, we are able to group responses
of a service to invalidate them later on more fine grained. this method resolves a
possible ``domain`` to allow grouping.

@return array of names of cache domains