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 android.content.Context; 20import java.io.Closeable; 21import java.io.File; 22import java.io.IOException; 23import java.net.CacheRequest; 24import java.net.CacheResponse; 25import java.net.ExtendedResponseCache; 26import java.net.HttpURLConnection; 27import java.net.ResponseCache; 28import java.net.ResponseSource; 29import java.net.URI; 30import java.net.URLConnection; 31import java.util.List; 32import java.util.Map; 33import javax.net.ssl.HttpsURLConnection; 34import libcore.io.DiskLruCache; 35import libcore.io.IoUtils; 36import org.apache.http.impl.client.DefaultHttpClient; 37 38/** 39 * Caches HTTP and HTTPS responses to the filesystem so they may be reused, 40 * saving time and bandwidth. This class supports {@link HttpURLConnection} and 41 * {@link HttpsURLConnection}; there is no platform-provided cache for {@link 42 * DefaultHttpClient} or {@link AndroidHttpClient}. 43 * 44 * <h3>Installing an HTTP response cache</h3> 45 * Enable caching of all of your application's HTTP requests by installing the 46 * cache at application startup. For example, this code installs a 10 MiB cache 47 * in the {@link Context#getCacheDir() application-specific cache directory} of 48 * the filesystem}: <pre> {@code 49 * protected void onCreate(Bundle savedInstanceState) { 50 * ... 51 * 52 * try { 53 * File httpCacheDir = new File(context.getCacheDir(), "http"); 54 * long httpCacheSize = 10 * 1024 * 1024; // 10 MiB 55 * HttpResponseCache.install(httpCacheDir, httpCacheSize); 56 * } catch (IOException e) { 57 * Log.i(TAG, "HTTP response cache installation failed:" + e); 58 * } 59 * } 60 * 61 * protected void onStop() { 62 * ... 63 * 64 * HttpResponseCache cache = HttpResponseCache.getInstalled(); 65 * if (cache != null) { 66 * cache.flush(); 67 * } 68 * }}</pre> 69 * This cache will evict entries as necessary to keep its size from exceeding 70 * 10 MiB. The best cache size is application specific and depends on the size 71 * and frequency of the files being downloaded. Increasing the limit may improve 72 * the hit rate, but it may also just waste filesystem space! 73 * 74 * <p>For some applications it may be preferable to create the cache in the 75 * external storage directory. <strong>There are no access controls on the 76 * external storage directory so it should not be used for caches that could 77 * contain private data.</strong> Although it often has more free space, 78 * external storage is optional and—even if available—can disappear 79 * during use. Retrieve the external cache directory using {@link 80 * Context#getExternalCacheDir()}. If this method returns null, your application 81 * should fall back to either not caching or caching on non-external storage. If 82 * the external storage is removed during use, the cache hit rate will drop to 83 * zero and ongoing cache reads will fail. 84 * 85 * <p>Flushing the cache forces its data to the filesystem. This ensures that 86 * all responses written to the cache will be readable the next time the 87 * activity starts. 88 * 89 * <h3>Cache Optimization</h3> 90 * To measure cache effectiveness, this class tracks three statistics: 91 * <ul> 92 * <li><strong>{@link #getRequestCount() Request Count:}</strong> the number 93 * of HTTP requests issued since this cache was created. 94 * <li><strong>{@link #getNetworkCount() Network Count:}</strong> the 95 * number of those requests that required network use. 96 * <li><strong>{@link #getHitCount() Hit Count:}</strong> the number of 97 * those requests whose responses were served by the cache. 98 * </ul> 99 * Sometimes a request will result in a conditional cache hit. If the cache 100 * contains a stale copy of the response, the client will issue a conditional 101 * {@code GET}. The server will then send either the updated response if it has 102 * changed, or a short 'not modified' response if the client's copy is still 103 * valid. Such responses increment both the network count and hit count. 104 * 105 * <p>The best way to improve the cache hit rate is by configuring the web 106 * server to return cacheable responses. Although this client honors all <a 107 * href="http://www.ietf.org/rfc/rfc2616.txt">HTTP/1.1 (RFC 2068)</a> cache 108 * headers, it doesn't cache partial responses. 109 * 110 * <h3>Force a Network Response</h3> 111 * In some situations, such as after a user clicks a 'refresh' button, it may be 112 * necessary to skip the cache, and fetch data directly from the server. To force 113 * a full refresh, add the {@code no-cache} directive: <pre> {@code 114 * connection.addRequestProperty("Cache-Control", "no-cache"); 115 * }</pre> 116 * If it is only necessary to force a cached response to be validated by the 117 * server, use the more efficient {@code max-age=0} instead: <pre> {@code 118 * connection.addRequestProperty("Cache-Control", "max-age=0"); 119 * }</pre> 120 * 121 * <h3>Force a Cache Response</h3> 122 * Sometimes you'll want to show resources if they are available immediately, 123 * but not otherwise. This can be used so your application can show 124 * <i>something</i> while waiting for the latest data to be downloaded. To 125 * restrict a request to locally-cached resources, add the {@code 126 * only-if-cached} directive: <pre> {@code 127 * try { 128 * connection.addRequestProperty("Cache-Control", "only-if-cached"); 129 * InputStream cached = connection.getInputStream(); 130 * // the resource was cached! show it 131 * } catch (FileNotFoundException e) { 132 * // the resource was not cached 133 * } 134 * }</pre> 135 * This technique works even better in situations where a stale response is 136 * better than no response. To permit stale cached responses, use the {@code 137 * max-stale} directive with the maximum staleness in seconds: <pre> {@code 138 * int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale 139 * connection.addRequestProperty("Cache-Control", "max-stale=" + maxStale); 140 * }</pre> 141 * 142 * <h3>Working With Earlier Releases</h3> 143 * This class was added in Android 4.0 (Ice Cream Sandwich). Use reflection to 144 * enable the response cache without impacting earlier releases: <pre> {@code 145 * try { 146 * File httpCacheDir = new File(context.getCacheDir(), "http"); 147 * long httpCacheSize = 10 * 1024 * 1024; // 10 MiB 148 * Class.forName("android.net.http.HttpResponseCache") 149 * .getMethod("install", File.class, long.class) 150 * .invoke(null, httpCacheDir, httpCacheSize); 151 * } catch (Exception httpResponseCacheNotAvailable) { 152 * }}</pre> 153 */ 154public final class HttpResponseCache extends ResponseCache 155 implements Closeable, ExtendedResponseCache { 156 157 private final libcore.net.http.HttpResponseCache delegate; 158 159 private HttpResponseCache(File directory, long maxSize) throws IOException { 160 this.delegate = new libcore.net.http.HttpResponseCache(directory, maxSize); 161 } 162 163 /** 164 * Returns the currently-installed {@code HttpResponseCache}, or null if 165 * there is no cache installed or it is not a {@code HttpResponseCache}. 166 */ 167 public static HttpResponseCache getInstalled() { 168 ResponseCache installed = ResponseCache.getDefault(); 169 return installed instanceof HttpResponseCache ? (HttpResponseCache) installed : null; 170 } 171 172 /** 173 * Creates a new HTTP response cache and {@link ResponseCache#setDefault 174 * sets it} as the system default cache. 175 * 176 * @param directory the directory to hold cache data. 177 * @param maxSize the maximum size of the cache in bytes. 178 * @return the newly-installed cache 179 * @throws IOException if {@code directory} cannot be used for this cache. 180 * Most applications should respond to this exception by logging a 181 * warning. 182 */ 183 public static HttpResponseCache install(File directory, long maxSize) throws IOException { 184 HttpResponseCache installed = getInstalled(); 185 if (installed != null) { 186 // don't close and reopen if an equivalent cache is already installed 187 DiskLruCache installedCache = installed.delegate.getCache(); 188 if (installedCache.getDirectory().equals(directory) 189 && installedCache.maxSize() == maxSize 190 && !installedCache.isClosed()) { 191 return installed; 192 } else { 193 IoUtils.closeQuietly(installed); 194 } 195 } 196 197 HttpResponseCache result = new HttpResponseCache(directory, maxSize); 198 ResponseCache.setDefault(result); 199 return result; 200 } 201 202 @Override public CacheResponse get(URI uri, String requestMethod, 203 Map<String, List<String>> requestHeaders) throws IOException { 204 return delegate.get(uri, requestMethod, requestHeaders); 205 } 206 207 @Override public CacheRequest put(URI uri, URLConnection urlConnection) throws IOException { 208 return delegate.put(uri, urlConnection); 209 } 210 211 /** 212 * Returns the number of bytes currently being used to store the values in 213 * this cache. This may be greater than the {@link #maxSize} if a background 214 * deletion is pending. 215 */ 216 public long size() { 217 return delegate.getCache().size(); 218 } 219 220 /** 221 * Returns the maximum number of bytes that this cache should use to store 222 * its data. 223 */ 224 public long maxSize() { 225 return delegate.getCache().maxSize(); 226 } 227 228 /** 229 * Force buffered operations to the filesystem. This ensures that responses 230 * written to the cache will be available the next time the cache is opened, 231 * even if this process is killed. 232 */ 233 public void flush() { 234 try { 235 delegate.getCache().flush(); 236 } catch (IOException ignored) { 237 } 238 } 239 240 /** 241 * Returns the number of HTTP requests that required the network to either 242 * supply a response or validate a locally cached response. 243 */ 244 public int getNetworkCount() { 245 return delegate.getNetworkCount(); 246 } 247 248 /** 249 * Returns the number of HTTP requests whose response was provided by the 250 * cache. This may include conditional {@code GET} requests that were 251 * validated over the network. 252 */ 253 public int getHitCount() { 254 return delegate.getHitCount(); 255 } 256 257 /** 258 * Returns the total number of HTTP requests that were made. This includes 259 * both client requests and requests that were made on the client's behalf 260 * to handle a redirects and retries. 261 */ 262 public int getRequestCount() { 263 return delegate.getRequestCount(); 264 } 265 266 /** @hide */ 267 @Override public void trackResponse(ResponseSource source) { 268 delegate.trackResponse(source); 269 } 270 271 /** @hide */ 272 @Override public void trackConditionalCacheHit() { 273 delegate.trackConditionalCacheHit(); 274 } 275 276 /** @hide */ 277 @Override public void update(CacheResponse conditionalCacheHit, HttpURLConnection connection) { 278 delegate.update(conditionalCacheHit, connection); 279 } 280 281 /** 282 * Uninstalls the cache and releases any active resources. Stored contents 283 * will remain on the filesystem. 284 */ 285 @Override public void close() throws IOException { 286 if (ResponseCache.getDefault() == this) { 287 ResponseCache.setDefault(null); 288 } 289 delegate.getCache().close(); 290 } 291 292 /** 293 * Uninstalls the cache and deletes all of its stored contents. 294 */ 295 public void delete() throws IOException { 296 if (ResponseCache.getDefault() == this) { 297 ResponseCache.setDefault(null); 298 } 299 delegate.getCache().delete(); 300 } 301} 302