Java tutorial
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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"); } }