/*
* Copyright 2006-2017 ICEsoft Technologies Canada Corp.
*
* 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 org.icepdf.core.util;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.LinkedHashMap;
/**
* Least recently used cache using SoftReferences.
*
* @since 5.0
*/
public class SoftLRUCache<K, V> {
private LinkedHashMap<K, SoftReference<V>> lruCache;
private ReferenceQueue<? super V> reqQueue;
public SoftLRUCache(int aInitialSize) {
lruCache = new LinkedHashMap<K, SoftReference<V>>(
aInitialSize,
0.75f,
true
);
reqQueue = new ReferenceQueue<V>();
}
public V get(K aKey) {
diposeStaleEntries();
SoftReference<V> ref = lruCache.get(aKey);
if (ref != null) {
return ref.get();
} else {
return null;
}
}
public V put(K aKey, V aValue) {
diposeStaleEntries();
SoftReference<V> oldValue = lruCache.put(aKey, new KeyReference<K, V>(aKey, aValue, reqQueue));
if (oldValue != null) {
return oldValue.get();
} else {
return null;
}
}
@SuppressWarnings("unchecked")
private void diposeStaleEntries() {
KeyReference<K, V> ref;
while ((ref = (KeyReference<K, V>) reqQueue.poll()) != null) {
lruCache.remove(ref.getKey());
}
}
public void clear() {
lruCache.clear();
}
private static class KeyReference<K, V> extends SoftReference<V> {
private K key;
public KeyReference(K key, V value, ReferenceQueue<? super V> refQueue) {
super(value, refQueue);
this.key = key;
}
public K getKey() {
return key;
}
}
}