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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 for cache entries that uses the
* popular Ehcache cache implementation.
* In particular, this backend allows for spillover to disk, where the
* cache can be effectively larger than memory, and cached responses are
* paged into and out of memory from disk as needed.
*
* N.B. Since the Ehcache is configured ahead of time with a
* maximum number of cache entries, this effectively ignores the
* {@link CacheConfig#setMaxCacheEntries(int) maximum cache entries}
* specified by a provided {@link CacheConfig}.
*
* Please refer to the
* Ehcache documentation for details on how to configure the Ehcache
* itself.
* @since 4.1
*/
public class EhcacheHttpCacheStorage implements HttpCacheStorage {
private final Ehcache cache;
private final HttpCacheEntrySerializer serializer;
private final int maxUpdateRetries;
/**
* Constructs a storage backend using the provided Ehcache
* with default configuration options.
* @param cache where to store cached origin responses
*/
public EhcacheHttpCacheStorage(final Ehcache cache) {
this(cache, CacheConfig.DEFAULT, new DefaultHttpCacheEntrySerializer());
}
/**
* Constructs a storage backend using the provided Ehcache
* with the given configuration options.
* @param cache where to store cached origin responses
* @param config cache storage configuration options - note that
* the setting for max object size will be ignored and
* should be configured in the Ehcache instead.
*/
public EhcacheHttpCacheStorage(final Ehcache cache, final CacheConfig config){
this(cache, config, new DefaultHttpCacheEntrySerializer());
}
/**
* Constructs a storage backend using the provided Ehcache
* with the given configuration options, but using an alternative
* cache entry serialization strategy.
* @param cache where to store cached origin responses
* @param config cache storage configuration options - note that
* the setting for max object size will be ignored and
* should be configured in the Ehcache instead.
* @param serializer alternative serialization mechanism
*/
public EhcacheHttpCacheStorage(final Ehcache cache, final CacheConfig config, final HttpCacheEntrySerializer serializer){
this.cache = cache;
this.maxUpdateRetries = config.getMaxUpdateRetries();
this.serializer = serializer;
}
@Override
public synchronized void putEntry(final String key, final HttpCacheEntry entry) throws IOException {
final ByteArrayOutputStream bos = new ByteArrayOutputStream();
serializer.writeTo(entry, bos);
cache.put(new Element(key, bos.toByteArray()));
}
@Override
public synchronized HttpCacheEntry getEntry(final String key) throws IOException {
final Element e = cache.get(key);
if(e == null){
return null;
}
final byte[] data = (byte[])e.getValue();
return serializer.readFrom(new ByteArrayInputStream(data));
}
@Override
public synchronized void removeEntry(final String key) {
cache.remove(key);
}
@Override
public synchronized void updateEntry(final String key, final HttpCacheUpdateCallback callback)
throws IOException, HttpCacheUpdateException {
int numRetries = 0;
do{
final Element oldElement = cache.get(key);
HttpCacheEntry existingEntry = null;
if(oldElement != null){
final byte[] data = (byte[])oldElement.getValue();
existingEntry = serializer.readFrom(new ByteArrayInputStream(data));
}
final HttpCacheEntry updatedEntry = callback.update(existingEntry);
if (existingEntry == null) {
putEntry(key, updatedEntry);
return;
} else {
// Attempt to do a CAS replace, if we fail then retry
// While this operation should work fine within this instance, multiple instances
// could trample each others' data
final ByteArrayOutputStream bos = new ByteArrayOutputStream();
serializer.writeTo(updatedEntry, bos);
final Element newElement = new Element(key, bos.toByteArray());
if (cache.replace(oldElement, newElement)) {
return;
}else{
numRetries++;
}
}
}while(numRetries <= maxUpdateRetries);
throw new HttpCacheUpdateException("Failed to update");
}
}