LinkedHashMap 를 이용한 LRU 캐쉬 구현

LinkedHashMap 를 이용하여 간단하게 LRU(leat-recently-used) 캐쉬를 구현할 수 있다.
여러가지 캐쉬 알고리즘과 솔루션들을 상황에 따라 고를 수 있지만, 간단한 캐쉬 기능이 필요한 경우
유용하게 쓸수 있다.

import java.util.LinkedHashMap;
import java.util.Collection;
import java.util.Map;
import java.util.ArrayList;
public class LRUCache<K,V> {
private static final float   hashTableLoadFactor = 0.75f;
private LinkedHashMap<K,V>   map;
private int                  cacheSize;

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; }}; }
/**
* The retrieved entry becomes the MRU (most recently used) entry.
*/
public synchronized V get (K key) {
   return map.get(key); }
/**
* If the cache is full, the LRU (least recently used) entry is dropped.
*/
public synchronized void put (K key, V value) {
   map.put (key,value); }
public synchronized void clear() {
   map.clear(); }
public synchronized int usedEntries() {
   return map.size(); }
public synchronized Collection<Map.Entry<K,V>> getAll() {
   return new ArrayList<Map.Entry<K,V>>(map.entrySet()); 
}

 
// 4test..!



public static void main (String[] args) {
    LRUCache<String,String> c = new LRUCache<String,String>(3);
    c.put ("1","one");                            // 1
    c.put ("2","two");                            // 2 1
    c.put ("3","three");                          // 3 2 1
    c.put ("4","four");                           // 4 3 2
    if (c.get("2")==null) throw new Error();      // 2 4 3
    c.put ("5","five");                           // 5 2 4
    c.put ("4","second four");                    // 4 5 2
    // Verify cache content.
    if (c.usedEntries() != 3)              throw new Error();
    if (!c.get("4").equals("second four")) throw new Error();
    if (!c.get("5").equals("five"))        throw new Error();
    if (!c.get("2").equals("two"))         throw new Error();
    // List cache content.
    for (Map.Entry<String,String> e : c.getAll())
       System.out.println (e.getKey() + " : " + e.getValue()); 
}

} 
 
참고: http://www.source-code.biz/snippets/java/6.htm
http://dojeun.egloos.com/317868
http://java.sun.com/j2se/1.4.2/docs/api/java/util/LinkedHashMap.html