private T updateConfig() {
        ts = file.getLastModified();
        try {
            ConfigPayload payload = new CfgConfigPayloadBuilder().deserialize(file.getContent());
            return payload.toInstance(configClass, key.getConfigId());
        } catch (IOException e) {
            throw new ConfigurationRuntimeException(e);
        }
    }
Subscription used when config id is file:...

@author Vegard Havdal
config/src/main/java/com/yahoo/config/subscription/impl/FileConfigSubscription.java