1/* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package android.net.http; 18 19import com.android.okhttp.Cache; 20import com.android.okhttp.AndroidShimResponseCache; 21import com.android.okhttp.OkCacheContainer; 22 23import java.io.Closeable; 24import java.io.File; 25import java.io.IOException; 26import java.net.CacheRequest; 27import java.net.CacheResponse; 28import java.net.ResponseCache; 29import java.net.URI; 30import java.net.URLConnection; 31import java.util.List; 32import java.util.Map; 33 34/** 35 * Caches HTTP and HTTPS responses to the filesystem so they may be reused, 36 * saving time and bandwidth. This class supports {@link 37 * java.net.HttpURLConnection} and {@link javax.net.ssl.HttpsURLConnection}; 38 * there is no platform-provided cache for {@code DefaultHttpClient} or 39 * {@code AndroidHttpClient}. Installation and instances are thread 40 * safe. 41 * 42 * <h3>Installing an HTTP response cache</h3> 43 * Enable caching of all of your application's HTTP requests by installing the 44 * cache at application startup. For example, this code installs a 10 MiB cache 45 * in the {@link android.content.Context#getCacheDir() application-specific 46 * cache directory} of the filesystem}: <pre> {@code 47 * protected void onCreate(Bundle savedInstanceState) { 48 * ... 49 * 50 * try { 51 * File httpCacheDir = new File(context.getCacheDir(), "http"); 52 * long httpCacheSize = 10 * 1024 * 1024; // 10 MiB 53 * HttpResponseCache.install(httpCacheDir, httpCacheSize); 54 * } catch (IOException e) { 55 * Log.i(TAG, "HTTP response cache installation failed:" + e); 56 * } 57 * } 58 * 59 * protected void onStop() { 60 * ... 61 * 62 * HttpResponseCache cache = HttpResponseCache.getInstalled(); 63 * if (cache != null) { 64 * cache.flush(); 65 * } 66 * }}</pre> 67 * This cache will evict entries as necessary to keep its size from exceeding 68 * 10 MiB. The best cache size is application specific and depends on the size 69 * and frequency of the files being downloaded. Increasing the limit may improve 70 * the hit rate, but it may also just waste filesystem space! 71 * 72 * <p>For some applications it may be preferable to create the cache in the 73 * external storage directory. <strong>There are no access controls on the 74 * external storage directory so it should not be used for caches that could 75 * contain private data.</strong> Although it often has more free space, 76 * external storage is optional and—even if available—can disappear 77 * during use. Retrieve the external cache directory using {@link 78 * android.content.Context#getExternalCacheDir()}. If this method returns null, 79 * your application should fall back to either not caching or caching on 80 * non-external storage. If the external storage is removed during use, the 81 * cache hit rate will drop to zero and ongoing cache reads will fail. 82 * 83 * <p>Flushing the cache forces its data to the filesystem. This ensures that 84 * all responses written to the cache will be readable the next time the 85 * activity starts. 86 * 87 * <h3>Cache Optimization</h3> 88 * To measure cache effectiveness, this class tracks three statistics: 89 * <ul> 90 * <li><strong>{@link #getRequestCount() Request Count:}</strong> the number 91 * of HTTP requests issued since this cache was created. 92 * <li><strong>{@link #getNetworkCount() Network Count:}</strong> the 93 * number of those requests that required network use. 94 * <li><strong>{@link #getHitCount() Hit Count:}</strong> the number of 95 * those requests whose responses were served by the cache. 96 * </ul> 97 * Sometimes a request will result in a conditional cache hit. If the cache 98 * contains a stale copy of the response, the client will issue a conditional 99 * {@code GET}. The server will then send either the updated response if it has 100 * changed, or a short 'not modified' response if the client's copy is still 101 * valid. Such responses increment both the network count and hit count. 102 * 103 * <p>The best way to improve the cache hit rate is by configuring the web 104 * server to return cacheable responses. Although this client honors all <a 105 * href="http://www.ietf.org/rfc/rfc2616.txt">HTTP/1.1 (RFC 2068)</a> cache 106 * headers, it doesn't cache partial responses. 107 * 108 * <h3>Force a Network Response</h3> 109 * In some situations, such as after a user clicks a 'refresh' button, it may be 110 * necessary to skip the cache, and fetch data directly from the server. To force 111 * a full refresh, add the {@code no-cache} directive: <pre> {@code 112 * connection.addRequestProperty("Cache-Control", "no-cache"); 113 * }</pre> 114 * If it is only necessary to force a cached response to be validated by the 115 * server, use the more efficient {@code max-age=0} instead: <pre> {@code 116 * connection.addRequestProperty("Cache-Control", "max-age=0"); 117 * }</pre> 118 * 119 * <h3>Force a Cache Response</h3> 120 * Sometimes you'll want to show resources if they are available immediately, 121 * but not otherwise. This can be used so your application can show 122 * <i>something</i> while waiting for the latest data to be downloaded. To 123 * restrict a request to locally-cached resources, add the {@code 124 * only-if-cached} directive: <pre> {@code 125 * try { 126 * connection.addRequestProperty("Cache-Control", "only-if-cached"); 127 * InputStream cached = connection.getInputStream(); 128 * // the resource was cached! show it 129 * } catch (FileNotFoundException e) { 130 * // the resource was not cached 131 * } 132 * }</pre> 133 * This technique works even better in situations where a stale response is 134 * better than no response. To permit stale cached responses, use the {@code 135 * max-stale} directive with the maximum staleness in seconds: <pre> {@code 136 * int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale 137 * connection.addRequestProperty("Cache-Control", "max-stale=" + maxStale); 138 * }</pre> 139 * 140 * <h3>Working With Earlier Releases</h3> 141 * This class was added in Android 4.0 (Ice Cream Sandwich). Use reflection to 142 * enable the response cache without impacting earlier releases: <pre> {@code 143 * try { 144 * File httpCacheDir = new File(context.getCacheDir(), "http"); 145 * long httpCacheSize = 10 * 1024 * 1024; // 10 MiB 146 * Class.forName("android.net.http.HttpResponseCache") 147 * .getMethod("install", File.class, long.class) 148 * .invoke(null, httpCacheDir, httpCacheSize); 149 * } catch (Exception httpResponseCacheNotAvailable) { 150 * }}</pre> 151 */ 152public final class HttpResponseCache extends ResponseCache implements Closeable, OkCacheContainer { 153 154 private final AndroidShimResponseCache delegate; 155 156 private HttpResponseCache(AndroidShimResponseCache delegate) { 157 this.delegate = delegate; 158 } 159 160 /** 161 * Returns the currently-installed {@code HttpResponseCache}, or null if 162 * there is no cache installed or it is not a {@code HttpResponseCache}. 163 */ 164 public static HttpResponseCache getInstalled() { 165 ResponseCache installed = ResponseCache.getDefault(); 166 if (installed instanceof HttpResponseCache) { 167 return (HttpResponseCache) installed; 168 } 169 return null; 170 } 171 172 /** 173 * Creates a new HTTP response cache and sets it as the system default cache. 174 * 175 * @param directory the directory to hold cache data. 176 * @param maxSize the maximum size of the cache in bytes. 177 * @return the newly-installed cache 178 * @throws IOException if {@code directory} cannot be used for this cache. 179 * Most applications should respond to this exception by logging a 180 * warning. 181 */ 182 public static synchronized HttpResponseCache install(File directory, long maxSize) 183 throws IOException { 184 ResponseCache installed = ResponseCache.getDefault(); 185 if (installed instanceof HttpResponseCache) { 186 HttpResponseCache installedResponseCache = (HttpResponseCache) installed; 187 // don't close and reopen if an equivalent cache is already installed 188 AndroidShimResponseCache trueResponseCache = installedResponseCache.delegate; 189 if (trueResponseCache.isEquivalent(directory, maxSize)) { 190 return installedResponseCache; 191 } else { 192 // The HttpResponseCache that owns this object is about to be replaced. 193 trueResponseCache.close(); 194 } 195 } 196 197 AndroidShimResponseCache trueResponseCache = 198 AndroidShimResponseCache.create(directory, maxSize); 199 HttpResponseCache newResponseCache = new HttpResponseCache(trueResponseCache); 200 ResponseCache.setDefault(newResponseCache); 201 return newResponseCache; 202 } 203 204 @Override public CacheResponse get(URI uri, String requestMethod, 205 Map<String, List<String>> requestHeaders) throws IOException { 206 return delegate.get(uri, requestMethod, requestHeaders); 207 } 208 209 @Override public CacheRequest put(URI uri, URLConnection urlConnection) throws IOException { 210 return delegate.put(uri, urlConnection); 211 } 212 213 /** 214 * Returns the number of bytes currently being used to store the values in 215 * this cache. This may be greater than the {@link #maxSize} if a background 216 * deletion is pending. {@code -1} is returned if the size cannot be determined. 217 */ 218 public long size() { 219 try { 220 return delegate.size(); 221 } catch (IOException e) { 222 // This can occur if the cache failed to lazily initialize. 223 return -1; 224 } 225 } 226 227 /** 228 * Returns the maximum number of bytes that this cache should use to store 229 * its data. 230 */ 231 public long maxSize() { 232 return delegate.maxSize(); 233 } 234 235 /** 236 * Force buffered operations to the filesystem. This ensures that responses 237 * written to the cache will be available the next time the cache is opened, 238 * even if this process is killed. 239 */ 240 public void flush() { 241 try { 242 delegate.flush(); 243 } catch (IOException ignored) { 244 } 245 } 246 247 /** 248 * Returns the number of HTTP requests that required the network to either 249 * supply a response or validate a locally cached response. 250 */ 251 public int getNetworkCount() { 252 return delegate.getNetworkCount(); 253 } 254 255 /** 256 * Returns the number of HTTP requests whose response was provided by the 257 * cache. This may include conditional {@code GET} requests that were 258 * validated over the network. 259 */ 260 public int getHitCount() { 261 return delegate.getHitCount(); 262 } 263 264 /** 265 * Returns the total number of HTTP requests that were made. This includes 266 * both client requests and requests that were made on the client's behalf 267 * to handle a redirects and retries. 268 */ 269 public int getRequestCount() { 270 return delegate.getRequestCount(); 271 } 272 273 /** 274 * Uninstalls the cache and releases any active resources. Stored contents 275 * will remain on the filesystem. 276 */ 277 @Override public void close() throws IOException { 278 if (ResponseCache.getDefault() == this) { 279 ResponseCache.setDefault(null); 280 } 281 delegate.close(); 282 } 283 284 /** 285 * Uninstalls the cache and deletes all of its stored contents. 286 */ 287 public void delete() throws IOException { 288 if (ResponseCache.getDefault() == this) { 289 ResponseCache.setDefault(null); 290 } 291 delegate.delete(); 292 } 293 294 /** @hide Needed for OkHttp integration. */ 295 @Override 296 public Cache getCache() { 297 return delegate.getCache(); 298 } 299 300} 301