/* * Copyright (C) 2011 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.net.http; import android.content.Context; import java.io.Closeable; import java.io.File; import java.io.IOException; import java.net.CacheRequest; import java.net.CacheResponse; import java.net.HttpURLConnection; import java.net.ResponseCache; import java.net.URI; import java.net.URLConnection; import java.util.List; import java.util.Map; import javax.net.ssl.HttpsURLConnection; import org.apache.http.impl.client.DefaultHttpClient; /** * Caches HTTP and HTTPS responses to the filesystem so they may be reused, * saving time and bandwidth. This class supports {@link HttpURLConnection} and * {@link HttpsURLConnection}; there is no platform-provided cache for {@link * DefaultHttpClient} or {@link AndroidHttpClient}. * *

Installing an HTTP response cache

* Enable caching of all of your application's HTTP requests by installing the * cache at application startup. For example, this code installs a 10 MiB cache * in the {@link Context#getCacheDir() application-specific cache directory} of * the filesystem}:
   {@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();
 *       }
 *   }}
* This cache will evict entries as necessary to keep its size from exceeding * 10 MiB. The best cache size is application specific and depends on the size * and frequency of the files being downloaded. Increasing the limit may improve * the hit rate, but it may also just waste filesystem space! * *

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 {@link * 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

* To measure cache effectiveness, this class tracks three statistics: * * Sometimes a request will result in a conditional cache hit. If the cache * contains a stale copy of the response, the client will issue a conditional * {@code GET}. The server will then send either the updated response if it has * changed, or a short 'not modified' response if the client's copy is still * valid. Such responses increment both the network count and hit count. * *

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

* In some situations, such as after a user clicks a 'refresh' button, it may be * necessary to skip the cache, and fetch data directly from the server. To force * a full refresh, add the {@code no-cache} directive:
   {@code
 *         connection.addRequestProperty("Cache-Control", "no-cache");
 * }
* If it is only necessary to force a cached response to be validated by the * server, use the more efficient {@code max-age=0} instead:
   {@code
 *         connection.addRequestProperty("Cache-Control", "max-age=0");
 * }
* *

Force a Cache Response

* Sometimes you'll want to show resources if they are available immediately, * but not otherwise. This can be used so your application can show * something while waiting for the latest data to be downloaded. To * restrict a request to locally-cached resources, add the {@code * only-if-cached} directive:
   {@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
 *     }
 * }
* This technique works even better in situations where a stale response is * better than no response. To permit stale cached responses, use the {@code * max-stale} directive with the maximum staleness in seconds:
   {@code
 *         int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
 *         connection.addRequestProperty("Cache-Control", "max-stale=" + maxStale);
 * }
* *

Working With Earlier Releases

* This class was added in Android 4.0 (Ice Cream Sandwich). Use reflection to * enable the response cache without impacting 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) {
 *       }}
*/ public final class HttpResponseCache extends ResponseCache implements Closeable { private final com.android.okhttp.HttpResponseCache delegate; private HttpResponseCache(com.android.okhttp.HttpResponseCache delegate) { this.delegate = delegate; } /** * Returns the currently-installed {@code HttpResponseCache}, or null if * there is no cache installed or it is not a {@code HttpResponseCache}. */ public static HttpResponseCache getInstalled() { ResponseCache installed = ResponseCache.getDefault(); if (installed instanceof com.android.okhttp.HttpResponseCache) { return new HttpResponseCache( (com.android.okhttp.HttpResponseCache) installed); } return null; } /** * Creates a new HTTP response cache and {@link ResponseCache#setDefault * sets it} as the system default cache. * * @param directory the directory to hold cache data. * @param maxSize the maximum size of the cache in bytes. * @return the newly-installed cache * @throws IOException if {@code directory} cannot be used for this cache. * Most applications should respond to this exception by logging a * warning. */ public static HttpResponseCache install(File directory, long maxSize) throws IOException { ResponseCache installed = ResponseCache.getDefault(); if (installed instanceof com.android.okhttp.HttpResponseCache) { com.android.okhttp.HttpResponseCache installedCache = (com.android.okhttp.HttpResponseCache) installed; // don't close and reopen if an equivalent cache is already installed if (installedCache.getDirectory().equals(directory) && installedCache.getMaxSize() == maxSize && !installedCache.isClosed()) { return new HttpResponseCache(installedCache); } else { // The HttpResponseCache that owns this object is about to be replaced. installedCache.close(); } } com.android.okhttp.HttpResponseCache responseCache = new com.android.okhttp.HttpResponseCache(directory, maxSize); ResponseCache.setDefault(responseCache); return new HttpResponseCache(responseCache); } @Override public CacheResponse get(URI uri, String requestMethod, Map> requestHeaders) throws IOException { return delegate.get(uri, requestMethod, requestHeaders); } @Override public CacheRequest put(URI uri, URLConnection urlConnection) throws IOException { return delegate.put(uri, urlConnection); } /** * Returns the number of bytes currently being used to store the values in * this cache. This may be greater than the {@link #maxSize} if a background * deletion is pending. */ public long size() { return delegate.getSize(); } /** * Returns the maximum number of bytes that this cache should use to store * its data. */ public long maxSize() { return delegate.getMaxSize(); } /** * Force buffered operations to the filesystem. This ensures that responses * written to the cache will be available the next time the cache is opened, * even if this process is killed. */ public void flush() { try { delegate.flush(); } catch (IOException ignored) { } } /** * Returns the number of HTTP requests that required the network to either * supply a response or validate a locally cached response. */ public int getNetworkCount() { return delegate.getNetworkCount(); } /** * Returns the number of HTTP requests whose response was provided by the * cache. This may include conditional {@code GET} requests that were * validated over the network. */ public int getHitCount() { return delegate.getHitCount(); } /** * Returns the total number of HTTP requests that were made. This includes * both client requests and requests that were made on the client's behalf * to handle a redirects and retries. */ public int getRequestCount() { return delegate.getRequestCount(); } /** * Uninstalls the cache and releases any active resources. Stored contents * will remain on the filesystem. */ @Override public void close() throws IOException { if (ResponseCache.getDefault() == this.delegate) { ResponseCache.setDefault(null); } delegate.close(); } /** * Uninstalls the cache and deletes all of its stored contents. */ public void delete() throws IOException { if (ResponseCache.getDefault() == this.delegate) { ResponseCache.setDefault(null); } delegate.delete(); } }