HttpResponseCache

class HttpResponseCache : ResponseCache, Closeable

Caches HTTP and HTTPS responses to the filesystem so they may be reused, saving time and bandwidth. This class supports and javax.net.ssl.HttpsURLConnection; there is no platform-provided cache for DefaultHttpClient or AndroidHttpClient. Installation and instances are thread safe.

Installing an HTTP response cache

<code>protected void onCreate(Bundle savedInstanceState) {
        ...
 
        try {
            File httpCacheDir = new File(context.getCacheDir(), "http");
            long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
            HttpResponseCache.install(httpCacheDir, httpCacheSize);
        } catch (IOException e) {
            Log.i(TAG, "HTTP response cache installation failed:" + e);
        }
    }
 
    protected void onStop() {
        ...
 
        HttpResponseCache cache = HttpResponseCache.getInstalled();
        if (cache != null) {
            cache.flush();
        }
    }</code>

For some applications it may be preferable to create the cache in the external storage directory. There are no access controls on the external storage directory so it should not be used for caches that could contain private data. Although it often has more free space, external storage is optional and—even if available—can disappear during use. Retrieve the external cache directory using android.content.Context#getExternalCacheDir(). If this method returns null, your application should fall back to either not caching or caching on non-external storage. If the external storage is removed during use, the cache hit rate will drop to zero and ongoing cache reads will fail.

Flushing the cache forces its data to the filesystem. This ensures that all responses written to the cache will be readable the next time the activity starts.

Cache Optimization

• Request Count: the number of HTTP requests issued since this cache was created.
• Network Count: the number of those requests that required network use.
• Hit Count: the number of those requests whose responses were served by the cache.

The best way to improve the cache hit rate is by configuring the web server to return cacheable responses. Although this client honors all HTTP/1.1 (RFC 2068) cache headers, it doesn't cache partial responses.

Force a Network Response

<code>connection.addRequestProperty("Cache-Control", "no-cache");
  </code>

<code>connection.addRequestProperty("Cache-Control", "max-age=0");
  </code>

Force a Cache Response

<code>try {
          connection.addRequestProperty("Cache-Control", "only-if-cached");
          InputStream cached = connection.getInputStream();
          // the resource was cached! show it
      } catch (FileNotFoundException e) {
          // the resource was not cached
      }
  </code>

<code>int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
          connection.addRequestProperty("Cache-Control", "max-stale=" + maxStale);
  </code>

Working With Earlier Releases

<code>try {
            File httpCacheDir = new File(context.getCacheDir(), "http");
            long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
            Class.forName("android.net.http.HttpResponseCache")
                    .getMethod("install", File.class, long.class)
                    .invoke(null, httpCacheDir, httpCacheSize);
        } catch (Exception httpResponseCacheNotAvailable) {
        }</code>

Summary

Public methods

fun close(): Unit

fun delete(): Unit

fun flush(): Unit

fun get(
    uri: URI!, 
    requestMethod: String!, 
    requestHeaders: MutableMap<String!, MutableList<String!>!>!
): CacheResponse!

fun getHitCount(): Int

static fun getInstalled(): HttpResponseCache!

fun getNetworkCount(): Int

fun getRequestCount(): Int

static fun install(
    directory: File!, 
    maxSize: Long
): HttpResponseCache!

fun maxSize(): Long

fun put(
    uri: URI!, 
    urlConnection: URLConnection!
): CacheRequest!

fun size(): Long