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Apache HttpComponents HttpClient - Cache
/*
* ====================================================================
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* 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
*
* This class is a storage backend that uses an external memcached
* for storing cached origin responses. This storage option provides a
* couple of interesting advantages over the default in-memory storage
* backend:
*
*
* - in-memory cached objects can survive an application restart since
* they are held in a separate process
* - it becomes possible for several cooperating applications to share
* a large memcached farm together
*
*
* 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
* KetamaConnectionFactory).
*
*
* 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
* caching HTTP client 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}.
*
*
*
* 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.
*
*
*
* Please refer to the
* memcached documentation and in particular to the documentation for
* the spymemcached
* documentation for details about how to set up and configure memcached
* and the Java client used here, respectively.
*
*
* @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 memcached 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 memcached daemon is running
* @throws IOException in case of an error
*/
public MemcachedHttpCacheStorage(final InetSocketAddress address) throws IOException {
this(new MemcachedClient(address));
}
/**
* Create a storage backend using the pre-configured given
* memcached client.
* @param cache client to use for communicating with memcached
*/
public MemcachedHttpCacheStorage(final MemcachedClientIF cache) {
this(cache, CacheConfig.DEFAULT, new MemcachedCacheEntryFactoryImpl(),
new SHA256KeyHashingScheme());
}
/**
* Create a storage backend using the given memcached client and
* applying the given cache configuration and cache entry serialization
* mechanism. Deprecation note: 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 memcached
* @param config apply HTTP cache-related options
* @param serializer ignored
*
* @deprecated (4.2) do not use
*/
@Deprecated
public MemcachedHttpCacheStorage(final MemcachedClientIF client, final CacheConfig config,
final HttpCacheEntrySerializer serializer) {
this(client, config, new MemcachedCacheEntryFactoryImpl(),
new SHA256KeyHashingScheme());
}
/**
* Create a storage backend using the given memcached client and
* applying the given cache configuration, serialization, and hashing
* mechanisms.
* @param client how to talk to memcached
* @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(final MemcachedClientIF client, final CacheConfig config,
final MemcachedCacheEntryFactory memcachedCacheEntryFactory,
final KeyHashingScheme keyHashingScheme) {
this.client = client;
this.maxUpdateRetries = config.getMaxUpdateRetries();
this.memcachedCacheEntryFactory = memcachedCacheEntryFactory;
this.keyHashingScheme = keyHashingScheme;
}
@Override
public void putEntry(final String url, final HttpCacheEntry entry) throws IOException {
final byte[] bytes = serializeEntry(url, entry);
final String key = getCacheKey(url);
if (key == null) {
return;
}
try {
client.set(key, 0, bytes);
} catch (final OperationTimeoutException ex) {
throw new MemcachedOperationTimeoutException(ex);
}
}
private String getCacheKey(final String url) {
try {
return keyHashingScheme.hash(url);
} catch (final MemcachedKeyHashingException mkhe) {
return null;
}
}
private byte[] serializeEntry(final String url, final HttpCacheEntry hce) throws IOException {
final MemcachedCacheEntry mce = memcachedCacheEntryFactory.getMemcachedCacheEntry(url, hce);
try {
return mce.toByteArray();
} catch (final MemcachedSerializationException mse) {
final IOException ioe = new IOException();
ioe.initCause(mse);
throw ioe;
}
}
private byte[] convertToByteArray(final 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(final Object o) {
final byte[] bytes = convertToByteArray(o);
if (bytes == null) {
return null;
}
final MemcachedCacheEntry mce = memcachedCacheEntryFactory.getUnsetCacheEntry();
try {
mce.set(bytes);
} catch (final MemcachedSerializationException mse) {
return null;
}
return mce;
}
@Override
public HttpCacheEntry getEntry(final String url) throws IOException {
final String key = getCacheKey(url);
if (key == null) {
return null;
}
try {
final MemcachedCacheEntry mce = reconstituteEntry(client.get(key));
if (mce == null || !url.equals(mce.getStorageKey())) {
return null;
}
return mce.getHttpCacheEntry();
} catch (final OperationTimeoutException ex) {
throw new MemcachedOperationTimeoutException(ex);
}
}
@Override
public void removeEntry(final String url) throws IOException {
final String key = getCacheKey(url);
if (key == null) {
return;
}
try {
client.delete(key);
} catch (final OperationTimeoutException ex) {
throw new MemcachedOperationTimeoutException(ex);
}
}
@Override
public void updateEntry(final String url, final HttpCacheUpdateCallback callback)
throws HttpCacheUpdateException, IOException {
int numRetries = 0;
final String key = getCacheKey(url);
if (key == null) {
throw new HttpCacheUpdateException("couldn't generate cache key");
}
do {
try {
final CASValue