package eu.europeana.cloud.service.dps.util;
import java.io.Serializable;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* An LRU cache, based on <code>LinkedHashMap</code>.
*
* <p>
* This cache has a fixed maximum number of elements (<code>cacheSize</code>).
* If the cache is full and another entry is added, the LRU (least recently
* used) entry is dropped.
*
*
* <p>
* Author: Christian d'Heureuse, Inventec Informatik AG, Zurich, Switzerland<br>
* Multi-licensed: EPL / LGPL / GPL / AL / BSD.
*/
public class LRUCache<K, V> implements Serializable {
private static final long serialVersionUID = 1L;
private static final float hashTableLoadFactor = 0.75f;
private int hits = 0;
private int miss = 0;
private LinkedHashMap<K, V> map;
private int cacheSize;
/**
* Creates a new LRU cache.
*
* @param cacheSize
* the maximum number of entries that will be kept in this cache.
*/
public LRUCache(int cacheSize) {
this.cacheSize = cacheSize;
int hashTableCapacity = (int) Math
.ceil(cacheSize / hashTableLoadFactor) + 1;
map = new LinkedHashMap<K, V>(hashTableCapacity, hashTableLoadFactor,
true) {
// (an anonymous inner class)
private static final long serialVersionUID = 1;
@Override
protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
return size() > LRUCache.this.cacheSize;
}
};
}
/**
* Retrieves an entry from the cache.<br>
* The retrieved entry becomes the MRU (most recently used) entry.
*
* @param key
* the key whose associated value is to be returned.
* @return the value associated to this key, or null if no value with this
* key exists in the cache.
*/
public V get(K key) {
return map.get(key);
}
/**
* Adds an entry to this cache. The new entry becomes the MRU (most recently
* used) entry. If an entry with the specified key already exists in the
* cache, it is replaced by the new entry. If the cache is full, the LRU
* (least recently used) entry is removed from the cache.
*
* @param key
* the key with which the specified value is to be associated.
* @param value
* a value to be associated with the specified key.
*/
public void put(K key, V value) {
map.put(key, value);
}
/**
* Clears the cache.
*/
public void clear() {
map.clear();
}
/**
* Returns the number of used entries in the cache.
*
* @return the number of entries currently in the cache.
*/
public int usedEntries() {
return map.size();
}
public boolean containsKey(K k){
if (map.containsKey(k)) {
hits++;
return true;
}
else{
miss++;
return false;
}
}
public double hitRate(){
return hits/(double)(hits+miss);
}
}