volley - json caching is not working properly

Question

Server sends me json object, expiration and ETAg.. I want to Voley save this object in cache and in next request for this object use request to the server including ETag in the header. If response will be 304 Not Modified, then it should use cached resource and if it will be 200 OK, it should use new resource from the server.

Volley doesn't send request at all (if the cache isn't expired) or if it is expired it sends new request with If-None-Match + etag string.. and server always response with 200

Answer 1

Volley will not issue a request to server at all if it detects that cache entry has not expired yet. Here are some code excerpts to prove it:

// If it is completely expired, just send it to the network.
if (entry.isExpired()) {
    request.addMarker("cache-hit-expired");
    request.setCacheEntry(entry);
    mNetworkQueue.put(request);
    continue;
}

And:

if (!entry.refreshNeeded()) {
    // Completely unexpired cache hit. Just deliver the response.
    mDelivery.postResponse(request, response);
} else {
    // Soft-expired cache hit. We can deliver the cached response,
    // but we need to also send the request to the network for
    // refreshing.
    request.addMarker("cache-hit-refresh-needed");
    request.setCacheEntry(entry);

    // Mark the response as intermediate.
    response.intermediate = true;

    // Post the intermediate response back to the user and have
    // the delivery then forward the request along to the network.
    mDelivery.postResponse(request, response, new Runnable() {
        @Override
        public void run() {
            try {
                mNetworkQueue.put(request);
            } catch (InterruptedException e) {
                // Not much we can do about this.
            }
        }
    });
}

You might want to control resource expiration on your server by setting max-age at Cache-Control or Expires headers in order to tweak cache on client side.