package org.apache.ojb.broker.cache;
/* Copyright 2004 The Apache Software Foundation
*
* 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.
*/
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.HashMap;
import java.util.Properties;
import org.apache.commons.collections.LRUMap;
import org.apache.ojb.broker.Identity;
import org.apache.ojb.broker.PersistenceBroker;
import org.apache.ojb.broker.cache.ObjectCache;
import org.apache.ojb.broker.util.configuration.Configurable;
import org.apache.ojb.broker.util.configuration.Configuration;
import org.apache.ojb.broker.util.configuration.ConfigurationException;
import org.apache.ojb.broker.util.configuration.impl.OjbConfigurator;
public class ObjectCacheSoftImpl implements ObjectCache, Configurable {
/**
* The static the cache map
*/
private static SoftHashMap cache = null;
/**
* The size of the cache
*/
private static int size = 10000;
/**
* Constructor called by ojb
* @param broker ignored parameter
* @param properties ignored parameter
*/
public ObjectCacheSoftImpl(PersistenceBroker broker, Properties properties)
{
if (cache == null) {
OjbConfigurator.getInstance().configure(this);
cache = new SoftHashMap(size);
}
}
/**
* @see
org.apache.ojb.broker.util.configuration.Configurable#configure(org.apache.o
jb.broker.util.configuration.Configuration)
*/
public void configure(Configuration configuration) throws
ConfigurationException {
size = configuration.getInteger("ObjectCacheSoftImpl", size);
}
/**
* @see
org.apache.ojb.broker.cache.ObjectCache#cache(org.apache.ojb.broker.Identity
, java.lang.Object)
*/
public void cache(Identity oid, Object obj) {
cache.put(oid, obj);
}
/**
* @see
org.apache.ojb.broker.cache.ObjectCache#lookup(org.apache.ojb.broker.Identit
y)
*/
public Object lookup(Identity oid) {
return cache.get(oid);
}
/**
* @see
org.apache.ojb.broker.cache.ObjectCache#remove(org.apache.ojb.broker.Identit
y)
*/
public void remove(Identity oid) {
cache.remove(oid);
}
/**
* @see org.apache.ojb.broker.cache.ObjectCache#clear()
*/
public void clear() {
cache.clear();
}
/**
* Kind of map using SoftReference to store values
*/
public static final class SoftHashMap {
/** The internal HashMap that will hold the SoftReference. */
private HashMap hash;
/** The FIFO list of hard references, order of last access. */
private LRUMap hardCacheMap;
/** Reference queue for cleared SoftReference objects. */
private ReferenceQueue queue;
/**
* Construct a new hash map with the specified size
* @param hardSize the maximum capacity of this map
*/
public SoftHashMap(final int hardSize) {
hash = new HashMap();
hardCacheMap = new LRUMap(hardSize);
queue = new ReferenceQueue();
}
/**
* Put the key, value pair into the HashMap using a SoftValue object
* @param key the key
* @param value the value
* @return the old value
*/
public Object put(Object key, Object value) {
//check null since hashtable doesn't support null key or null
value
if (key == null || value == null) {
return null;
}
processQueue(); // throw out garbage collected values first
hardCacheMap.put(key, value);
return hash.put(key, new SoftValue(value, key, queue));
}
/**
* Retrieve the value associated to a given key
* @param key the key
* @return the value associated to this key
*/
public Object get(Object key) {
// Check null since Hashtable doesn't support null key or null
value
if (key == null) {
return null;
}
Object result = null;
// We get the SoftReference represented by that key
SoftReference softRef = (SoftReference) hash.get(key);
if (softRef != null) {
result = softRef.get();
if (result == null) {
// If the value has been garbage collected,
remove the
// entry from the HashMap.
hash.remove(key);
} else {
if (!hardCacheMap.containsKey(key)) {
hardCacheMap.put(key, result);
} else {
hardCacheMap.get(key);
}
}
}
return result;
}
/**
* Remove the entry for this key
* @param key the key
* @return the old value
*/
public Object remove(Object key) {
processQueue(); // throw out garbage collected values first
Object retval = null;
Object value = hash.remove(key);
if (value != null) {
if (value instanceof SoftValue) {
retval = ((SoftValue) value).get();
}
}
return retval;
}
/**
* Clear the map
*/
public void clear() {
processQueue();
hash.clear();
hardCacheMap.clear();
}
/**
* Class derived from SoftReference, used to
* store the key of the map.
*/
private class SoftValue extends SoftReference {
/** the key */
private final Object key; // always make data member final
/**
* Create a SoftValue given the object, key and queue
* @param k the object
* @param key the key
* @param q the reference queue
*/
private SoftValue(final Object k, final Object key, final
ReferenceQueue
q) {
super(k, q);
this.key = key;
}
}
/**
* Removes keys and objects that have been garbaged
*/
private void processQueue() {
SoftValue sv;
while ((sv = (SoftValue) queue.poll()) != null) {
hash.remove(sv.key); // we can access private data!
}
}
}
}
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