@Override
    public void onException(Exception e) {
        if (Log.isLoggable(TAG, Log.DEBUG)) {
            Log.d(TAG, "load failed", e);
        }

        status = Status.FAILED;
        //TODO: what if this is a thumbnail request?
        if (requestListener == null || !requestListener.onException(e, model, target, isFirstReadyResource())) {
            setErrorPlaceholder(e);
        }
    }
A callback method that should never be invoked directly.
core/src/main/java/com/bumptech/glide/request/GenericRequest.java