/*
* 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}.
*
* <h3>Installing an HTTP response cache</h3>
* 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}: <pre> {@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();
* }
* }}</pre>
* 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!
*
* <p>For some applications it may be preferable to create the cache in the
* external storage directory. <strong>There are no access controls on the
* external storage directory so it should not be used for caches that could
* contain private data.</strong> 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.
*
* <p>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.
*
* <h3>Cache Optimization</h3>
* To measure cache effectiveness, this class tracks three statistics:
* <ul>
* <li><strong>{@link #getRequestCount() Request Count:}</strong> the number
* of HTTP requests issued since this cache was created.
* <li><strong>{@link #getNetworkCount() Network Count:}</strong> the
* number of those requests that required network use.
* <li><strong>{@link #getHitCount() Hit Count:}</strong> the number of
* those requests whose responses were served by the cache.
* </ul>
* 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.
*
* <p>The best way to improve the cache hit rate is by configuring the web
* server to return cacheable responses. Although this client honors all <a
* href="http://www.ietf.org/rfc/rfc2616.txt">HTTP/1.1 (RFC 2068)</a> cache
* headers, it doesn't cache partial responses.
*
* <h3>Force a Network Response</h3>
* 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: <pre> {@code
* connection.addRequestProperty("Cache-Control", "no-cache");
* }</pre>
* 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: <pre> {@code
* connection.addRequestProperty("Cache-Control", "max-age=0");
* }</pre>
*
* <h3>Force a Cache Response</h3>
* Sometimes you'll want to show resources if they are available immediately,
* but not otherwise. This can be used so your application can show
* <i>something</i> while waiting for the latest data to be downloaded. To
* restrict a request to locally-cached resources, add the {@code
* only-if-cached} directive: <pre> {@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
* }
* }</pre>
* 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: <pre> {@code
* int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
* connection.addRequestProperty("Cache-Control", "max-stale=" + maxStale);
* }</pre>
*
* <h3>Working With Earlier Releases</h3>
* This class was added in Android 4.0 (Ice Cream Sandwich). Use reflection to
* enable the response cache without impacting earlier releases: <pre> {@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) {
* }}</pre>
*/
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<String, List<String>> 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();
}
}
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