HttpResponseCache

public final class HttpResponseCache
extends ResponseCache implements Closeable, OkCacheContainer

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

Installing an HTTP response cache

   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();
       }
   }

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 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

   connection.addRequestProperty("Cache-Control", "no-cache");
 

   connection.addRequestProperty("Cache-Control", "max-age=0");
 

Force a Cache Response

   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
     }
 

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

Working With Earlier Releases

   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) {
       }

Summary

Inherited methods
From class java.net.ResponseCache abstract CacheResponse get(URI uri, String rqstMethod, Map<String, List<String>> rqstHeaders) Retrieve the cached response based on the requesting uri, request method and request headers. static ResponseCache getDefault() Gets the system-wide response cache. abstract CacheRequest put(URI uri, URLConnection conn) The protocol handler calls this method after a resource has been retrieved, and the ResponseCache must decide whether or not to store the resource in its cache. static void setDefault(ResponseCache responseCache) Sets (or unsets) the system-wide cache.
From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long millis, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long millis) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.
From interface java.io.Closeable abstract void close() Closes this stream and releases any system resources associated with it.
From interface com.android.okhttp.OkCacheContainer abstract Cache getCache()
From interface java.lang.AutoCloseable abstract void close() Closes this resource, relinquishing any underlying resources.

Public methods

void close ()

void delete ()

void flush ()

CacheResponse get (URI uri, 
                String requestMethod, 
                Map<String, List<String>> requestHeaders)

int getHitCount ()

HttpResponseCache getInstalled ()

int getNetworkCount ()

int getRequestCount ()

HttpResponseCache install (File directory, 
                long maxSize)

long maxSize ()

CacheRequest put (URI uri, 
                URLConnection urlConnection)

long size ()