/*
* ====================================================================
* 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
* <http://www.apache.org/>.
*
*/
package org.apache.http.impl.client.cache.memcached;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
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 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.DefaultHttpCacheEntrySerializer;
/**
* <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, effectively providing cache
* peering of a sort</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>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 final MemcachedClientIF client;
private final HttpCacheEntrySerializer serializer;
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
*/
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 DefaultHttpCacheEntrySerializer());
}
/**
* Create a storage backend using the given <i>memcached</i> client and
* applying the given cache configuration and cache entry serialization
* mechanism.
* @param client how to talk to <i>memcached</i>
* @param config apply HTTP cache-related options
* @param serializer how to serialize the cache entries before writing
* them out to <i>memcached</i>. The provided {@link
* DefaultHttpCacheEntrySerializer} is a fine serialization mechanism
* to use here.
*/
public MemcachedHttpCacheStorage(MemcachedClientIF client, CacheConfig config,
HttpCacheEntrySerializer serializer) {
this.client = client;
this.maxUpdateRetries = config.getMaxUpdateRetries();
this.serializer = serializer;
}
public void putEntry(String url, HttpCacheEntry entry) throws IOException {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
serializer.writeTo(entry, bos);
client.set(url, 0, bos.toByteArray());
}
public HttpCacheEntry getEntry(String url) throws IOException {
byte[] data = (byte[]) client.get(url);
if (null == data)
return null;
InputStream bis = new ByteArrayInputStream(data);
return serializer.readFrom(bis);
}
public void removeEntry(String url) throws IOException {
client.delete(url);
}
public void updateEntry(String url, HttpCacheUpdateCallback callback)
throws HttpCacheUpdateException, IOException {
int numRetries = 0;
do{
CASValue<Object> v = client.gets(url);
byte[] oldBytes = (v != null) ? (byte[]) v.getValue() : null;
HttpCacheEntry existingEntry = null;
if (oldBytes != null) {
ByteArrayInputStream bis = new ByteArrayInputStream(oldBytes);
existingEntry = serializer.readFrom(bis);
}
HttpCacheEntry updatedEntry = callback.update(existingEntry);
if (v == null) {
putEntry(url, updatedEntry);
return;
} else {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
serializer.writeTo(updatedEntry, bos);
CASResponse casResult = client.cas(url, v.getCas(), bos.toByteArray());
if (casResult != CASResponse.OK) {
numRetries++;
}
else return;
}
} while(numRetries <= maxUpdateRetries);
throw new HttpCacheUpdateException("Failed to update");
}
}