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* ====================================================================
* Licensed to the Apache Software Foundation (ASF) under one
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* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.http.impl.client.cache.memcached;
import java.io.IOException;
import java.net.InetSocketAddress;
import net.spy.memcached.CASResponse;
import net.spy.memcached.CASValue;
import net.spy.memcached.MemcachedClient;
import net.spy.memcached.MemcachedClientIF;
import net.spy.memcached.OperationTimeoutException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.http.client.cache.HttpCacheEntry;
import org.apache.http.client.cache.HttpCacheEntrySerializer;
import org.apache.http.client.cache.HttpCacheUpdateException;
import org.apache.http.client.cache.HttpCacheStorage;
import org.apache.http.client.cache.HttpCacheUpdateCallback;
import org.apache.http.impl.client.cache.CacheConfig;
import org.apache.http.impl.client.cache.CachingHttpClient;
/**
* <p>This class is a storage backend that uses an external <i>memcached</i>
* for storing cached origin responses. This storage option provides a
* couple of interesting advantages over the default in-memory storage
* backend:
* <ol>
* <li>in-memory cached objects can survive an application restart since
* they are held in a separate process</li>
* <li>it becomes possible for several cooperating applications to share
* a large <i>memcached</i> farm together</li>
* </ol>
* Note that in a shared memcached pool setting you may wish to make use
* of the Ketama consistent hashing algorithm to reduce the number of
* cache misses that might result if one of the memcached cluster members
* fails (see the <a href="http://dustin.github.com/java-memcached-client/apidocs/net/spy/memcached/KetamaConnectionFactory.html">
* KetamaConnectionFactory</a>).
* </p>
*
* <p>Because memcached places limits on the size of its keys, we need to
* introduce a key hashing scheme to map the annotated URLs the higher-level
* {@link CachingHttpClient} wants to use as keys onto ones that are suitable
* for use with memcached. Please see {@link KeyHashingScheme} if you would
* like to use something other than the provided {@link SHA256KeyHashingScheme}.</p>
*
* <p>Because this hashing scheme can potentially result in key collisions (though
* highly unlikely), we need to store the higher-level logical storage key along
* with the {@link HttpCacheEntry} so that we can re-check it on retrieval. There
* is a default serialization scheme provided for this, although you can provide
* your own implementations of {@link MemcachedCacheEntry} and
* {@link MemcachedCacheEntryFactory} to customize this serialization.</p>
*
* <p>Please refer to the <a href="http://code.google.com/p/memcached/wiki/NewStart">
* memcached documentation</a> and in particular to the documentation for
* the <a href="http://code.google.com/p/spymemcached/">spymemcached
* documentation</a> for details about how to set up and configure memcached
* and the Java client used here, respectively.</p>
*
* @since 4.1
*/
public class MemcachedHttpCacheStorage implements HttpCacheStorage {
private static final Log log = LogFactory.getLog(MemcachedHttpCacheStorage.class);
private final MemcachedClientIF client;
private final KeyHashingScheme keyHashingScheme;
private final MemcachedCacheEntryFactory memcachedCacheEntryFactory;
private final int maxUpdateRetries;
/**
* Create a storage backend talking to a <i>memcached</i> instance
* listening on the specified host and port. This is useful if you
* just have a single local memcached instance running on the same
* machine as your application, for example.
* @param address where the <i>memcached</i> daemon is running
* @throws IOException in case of an error
*/
public MemcachedHttpCacheStorage(InetSocketAddress address) throws IOException {
this(new MemcachedClient(address));
}
/**
* Create a storage backend using the pre-configured given
* <i>memcached</i> client.
* @param cache client to use for communicating with <i>memcached</i>
*/
public MemcachedHttpCacheStorage(MemcachedClientIF cache) {
this(cache, new CacheConfig(), new MemcachedCacheEntryFactoryImpl(),
new SHA256KeyHashingScheme());
}
/**
* Create a storage backend using the given <i>memcached</i> client and
* applying the given cache configuration and cache entry serialization
* mechanism. <b>Deprecation note:</b> In the process of fixing a bug
* based on the need to hash logical storage keys onto memcached cache
* keys, the serialization process was revamped. This constructor still
* works, but the serializer argument will be ignored and default
* implementations of the new framework will be used. You can still
* provide custom serialization by using the
* {@link #MemcachedHttpCacheStorage(MemcachedClientIF, CacheConfig,
* MemcachedCacheEntryFactory, KeyHashingScheme)} constructor.
* @param client how to talk to <i>memcached</i>
* @param config apply HTTP cache-related options
* @param serializer <b>ignored</b>
*
* @deprecated (4.2) do not use
*/
@Deprecated
public MemcachedHttpCacheStorage(MemcachedClientIF client, CacheConfig config,
HttpCacheEntrySerializer serializer) {
this(client, config, new MemcachedCacheEntryFactoryImpl(),
new SHA256KeyHashingScheme());
}
/**
* Create a storage backend using the given <i>memcached</i> client and
* applying the given cache configuration, serialization, and hashing
* mechanisms.
* @param client how to talk to <i>memcached</i>
* @param config apply HTTP cache-related options
* @param memcachedCacheEntryFactory Factory pattern used for obtaining
* instances of alternative cache entry serialization mechanisms
* @param keyHashingScheme how to map higher-level logical "storage keys"
* onto "cache keys" suitable for use with memcached
*/
public MemcachedHttpCacheStorage(MemcachedClientIF client, CacheConfig config,
MemcachedCacheEntryFactory memcachedCacheEntryFactory,
KeyHashingScheme keyHashingScheme) {
this.client = client;
this.maxUpdateRetries = config.getMaxUpdateRetries();
this.memcachedCacheEntryFactory = memcachedCacheEntryFactory;
this.keyHashingScheme = keyHashingScheme;
}
public void putEntry(String url, HttpCacheEntry entry) throws IOException {
byte[] bytes = serializeEntry(url, entry);
String key = getCacheKey(url);
if (key == null) return;
try {
client.set(key, 0, bytes);
} catch (OperationTimeoutException ex) {
throw new MemcachedOperationTimeoutException(ex);
}
}
private String getCacheKey(String url) {
try {
return keyHashingScheme.hash(url);
} catch (MemcachedKeyHashingException mkhe) {
return null;
}
}
private byte[] serializeEntry(String url, HttpCacheEntry hce) throws IOException {
MemcachedCacheEntry mce = memcachedCacheEntryFactory.getMemcachedCacheEntry(url, hce);
try {
return mce.toByteArray();
} catch (MemcachedSerializationException mse) {
IOException ioe = new IOException();
ioe.initCause(mse);
throw ioe;
}
}
private byte[] convertToByteArray(Object o) {
if (o == null) return null;
if (!(o instanceof byte[])) {
log.warn("got a non-bytearray back from memcached: " + o);
return null;
}
return (byte[])o;
}
private MemcachedCacheEntry reconstituteEntry(Object o) throws IOException {
byte[] bytes = convertToByteArray(o);
if (bytes == null) return null;
MemcachedCacheEntry mce = memcachedCacheEntryFactory.getUnsetCacheEntry();
try {
mce.set(bytes);
} catch (MemcachedSerializationException mse) {
return null;
}
return mce;
}
public HttpCacheEntry getEntry(String url) throws IOException {
String key = getCacheKey(url);
if (key == null) return null;
try {
MemcachedCacheEntry mce = reconstituteEntry(client.get(key));
if (mce == null || !url.equals(mce.getStorageKey())) return null;
return mce.getHttpCacheEntry();
} catch (OperationTimeoutException ex) {
throw new MemcachedOperationTimeoutException(ex);
}
}
public void removeEntry(String url) throws IOException {
String key = getCacheKey(url);
if (key == null) return;
try {
client.delete(key);
} catch (OperationTimeoutException ex) {
throw new MemcachedOperationTimeoutException(ex);
}
}
public void updateEntry(String url, HttpCacheUpdateCallback callback)
throws HttpCacheUpdateException, IOException {
int numRetries = 0;
String key = getCacheKey(url);
if (key == null) {
throw new HttpCacheUpdateException("couldn't generate cache key");
}
do {
try {
CASValue<Object> v = client.gets(key);
MemcachedCacheEntry mce = (v == null) ? null
: reconstituteEntry(v.getValue());
if (mce != null && (!url.equals(mce.getStorageKey()))) {
mce = null;
}
HttpCacheEntry existingEntry = (mce == null) ? null
: mce.getHttpCacheEntry();
HttpCacheEntry updatedEntry = callback.update(existingEntry);
if (existingEntry == null) {
putEntry(url, updatedEntry);
return;
} else {
byte[] updatedBytes = serializeEntry(url, updatedEntry);
CASResponse casResult = client.cas(key, v.getCas(),
updatedBytes);
if (casResult != CASResponse.OK) {
numRetries++;
} else return;
}
} catch (OperationTimeoutException ex) {
throw new MemcachedOperationTimeoutException(ex);
}
} while (numRetries <= maxUpdateRetries);
throw new HttpCacheUpdateException("Failed to update");
}
}