com.phloc.commons.cache.convert.SimpleCacheWithConversion Maven / Gradle / Ivy
/**
* Copyright (C) 2006-2015 phloc systems
* http://www.phloc.com
* office[at]phloc[dot]com
*
* Licensed 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.
*/
package com.phloc.commons.cache.convert;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.ThreadSafe;
import com.phloc.commons.cache.AbstractCache;
import com.phloc.commons.convert.IUnidirectionalConverter;
/**
* A special cache that can create the value to be cache automatically from the
* key.
*
* @author Philip Helger
* @param
* Cache key type
* @param
* Cache value type
*/
@ThreadSafe
public class SimpleCacheWithConversion extends AbstractCache
{
public SimpleCacheWithConversion (@Nonnull final String sCacheName)
{
super (sCacheName);
}
/**
* Get the value from the cache. If no value is yet in the cache, the passed
* converter is used to get the value to cache.
*
* @param aKey
* The key of the cached object. May not be null.
* @param aValueRetriever
* The converter to be used to retrieve the object to cache. May not be
* null. This converter may not return null
* objects to cache!
* @return The cached value. Never null.
*/
@Nonnull
public final VALUETYPE getFromCache (@Nonnull final KEYTYPE aKey,
@Nonnull final IUnidirectionalConverter aValueRetriever)
{
// Already in the cache?
VALUETYPE aValue = super.getFromCacheNoStats (aKey);
if (aValue == null)
{
// No old value in the cache
m_aRWLock.writeLock ().lock ();
try
{
// Read again, in case the value was set between the two locking
// sections
// Note: do not increase statistics in this second try
aValue = super.getFromCacheNoStatsNotLocked (aKey);
if (aValue == null)
{
// Get the value to cache
aValue = aValueRetriever.convert (aKey);
// We cannot cache null values!
if (aValue == null)
throw new IllegalStateException ("The converter returned a null object for the key '" + aKey + "'");
super.putInCacheNotLocked (aKey, aValue);
m_aCacheAccessStats.cacheMiss ();
}
else
m_aCacheAccessStats.cacheHit ();
}
finally
{
m_aRWLock.writeLock ().unlock ();
}
}
else
m_aCacheAccessStats.cacheHit ();
return aValue;
}
}