HttpResponseCache.java revision 98e8b19c7bc422600a7a27819311d0059b5af2da
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.HttpURLConnection; 26import java.net.ResponseCache; 27import java.net.URI; 28import java.net.URLConnection; 29import java.util.List; 30import java.util.Map; 31import javax.net.ssl.HttpsURLConnection; 32import libcore.io.DiskLruCache; 33import libcore.io.IoUtils; 34import org.apache.http.impl.client.DefaultHttpClient; 35 36/** 37 * Caches HTTP and HTTPS responses to the filesystem so they may be reused, 38 * saving time and bandwidth. This class supports {@link HttpURLConnection} and 39 * {@link HttpsURLConnection}; there is no platform-provided cache for {@link 40 * DefaultHttpClient} or {@link AndroidHttpClient}. 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 Context#getCacheDir() application-specific cache directory} of 46 * 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 * Context#getExternalCacheDir()}. If this method returns null, your application 79 * should fall back to either not caching or caching on non-external storage. If 80 * the external storage is removed during use, the cache hit rate will drop to 81 * 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 */ 140public final class HttpResponseCache extends ResponseCache implements Closeable { 141 142 private final libcore.net.http.HttpResponseCache delegate; 143 144 private HttpResponseCache(File directory, long maxSize) throws IOException { 145 this.delegate = new libcore.net.http.HttpResponseCache(directory, maxSize); 146 } 147 148 /** 149 * Returns the currently-installed {@code HttpResponseCache}, or null if 150 * there is no cache installed or it is not a {@code HttpResponseCache}. 151 */ 152 public static HttpResponseCache getInstalled() { 153 ResponseCache installed = ResponseCache.getDefault(); 154 return installed instanceof HttpResponseCache ? (HttpResponseCache) installed : null; 155 } 156 157 /** 158 * Creates a new HTTP response cache and {@link ResponseCache#setDefault 159 * sets it} as the system default cache. 160 * 161 * @param directory the directory to hold cache data. 162 * @param maxSize the maximum size of the cache in bytes. 163 * @return the newly-installed cache 164 * @throws IOException if {@code directory} cannot be used for this cache. 165 * Most applications should respond to this exception by logging a 166 * warning. 167 */ 168 public static HttpResponseCache install(File directory, long maxSize) throws IOException { 169 HttpResponseCache installed = getInstalled(); 170 if (installed != null) { 171 // don't close and reopen if an equivalent cache is already installed 172 DiskLruCache installedCache = installed.delegate.getCache(); 173 if (installedCache.getDirectory().equals(directory) 174 && installedCache.maxSize() == maxSize 175 && !installedCache.isClosed()) { 176 return installed; 177 } else { 178 IoUtils.closeQuietly(installed); 179 } 180 } 181 182 HttpResponseCache result = new HttpResponseCache(directory, maxSize); 183 ResponseCache.setDefault(result); 184 return result; 185 } 186 187 @Override public CacheResponse get(URI uri, String requestMethod, 188 Map<String, List<String>> requestHeaders) throws IOException { 189 return delegate.get(uri, requestMethod, requestHeaders); 190 } 191 192 @Override public CacheRequest put(URI uri, URLConnection urlConnection) throws IOException { 193 return delegate.put(uri, urlConnection); 194 } 195 196 /** 197 * Returns the number of bytes currently being used to store the values in 198 * this cache. This may be greater than the {@link #maxSize} if a background 199 * deletion is pending. 200 */ 201 public long size() { 202 return delegate.getCache().size(); 203 } 204 205 /** 206 * Returns the maximum number of bytes that this cache should use to store 207 * its data. 208 */ 209 public long maxSize() { 210 return delegate.getCache().maxSize(); 211 } 212 213 /** 214 * Force buffered operations to the filesystem. This ensures that responses 215 * written to the cache will be available the next time the cache is opened, 216 * even if this process is killed. 217 */ 218 public void flush() { 219 try { 220 delegate.getCache().flush(); 221 } catch (IOException ignored) { 222 } 223 } 224 225 /** 226 * Returns the number of HTTP requests that required the network to either 227 * supply a response or validate a locally cached response. 228 */ 229 public int getNetworkCount() { 230 return delegate.getNetworkCount(); 231 } 232 233 /** 234 * Returns the number of HTTP requests whose response was provided by the 235 * cache. This may include conditional {@code GET} requests that were 236 * validated over the network. 237 */ 238 public int getHitCount() { 239 return delegate.getHitCount(); 240 } 241 242 /** 243 * Returns the total number of HTTP requests that were made. This includes 244 * both client requests and requests that were made on the client's behalf 245 * to handle a redirects and retries. 246 */ 247 public int getRequestCount() { 248 return delegate.getRequestCount(); 249 } 250 251 /** 252 * Uninstalls the cache and releases any active resources. Stored contents 253 * will remain on the filesystem. 254 */ 255 @Override public void close() throws IOException { 256 if (ResponseCache.getDefault() == this) { 257 ResponseCache.setDefault(null); 258 } 259 delegate.getCache().close(); 260 } 261 262 /** 263 * Uninstalls the cache and deletes all of its stored contents. 264 */ 265 public void delete() throws IOException { 266 if (ResponseCache.getDefault() == this) { 267 ResponseCache.setDefault(null); 268 } 269 delegate.getCache().delete(); 270 } 271} 272