java几种缓存的简单实现

1，先进先出FIFO

package chin.tei.fifo;

import java.util.LinkedHashMap;

public class CacheFIFO extends LinkedHashMap{
		
	private static final long serialVersionUID = -1942463383036528618L;
	private final int maxCapacity;

	public CacheFIFO(int maxCapacity) {
		super();                                            // 默认为插入顺序
		this.maxCapacity = maxCapacity;
	}

    @Override
    protected boolean removeEldestEntry(java.util.Map.Entry eldest) {
        return size() > maxCapacity;                               // 超过最大缓存数就删除最先插入的元素
    }
    
    public int getMaxCapacity() {
    	return this.maxCapacity;
    }
}

2，LRU( 最近最少使用删除原则）

import java.util.LinkedHashMap;
import java.util.Collection;
import java.util.Map;
import java.util.ArrayList;

/**
* An LRU cache, based on LinkedHashMap.
*
* 

* This cache has a fixed maximum number of elements (cacheSize).
* If the cache is full and another entry is added, the LRU (least recently used) entry is dropped.
*
* 

* This class is thread-safe. All methods of this class are synchronized.
*
* 

* Author: Christian d'Heureuse, Inventec Informatik AG, Zurich, Switzerland

* Multi-licensed: EPL / LGPL / GPL / AL / BSD.
*/
public class LRUCache {

private static final float   hashTableLoadFactor = 0.75f;

private LinkedHashMap   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(hashTableCapacity, hashTableLoadFactor, true) {
      // (an anonymous inner class)
      private static final long serialVersionUID = 1;
      @Override protected boolean removeEldestEntry (Map.Entry eldest) {
         return size() > LRUCache.this.cacheSize; }}; }

/**
* Retrieves an entry from the cache.

* 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 synchronized 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 synchronized void put (K key, V value) {
   map.put (key, value); }

/**
* Clears the cache.
*/
public synchronized void clear() {
   map.clear(); }

/**
* Returns the number of used entries in the cache.
* @return the number of entries currently in the cache.
*/
public synchronized int usedEntries() {
   return map.size(); }

/**
* Returns a Collection that contains a copy of all cache entries.
* @return a Collection with a copy of the cache content.
*/
public synchronized Collection> getAll() {
   return new ArrayList>(map.entrySet()); }

} // end class LRUCache
------------------------------------------------------------------------------------------
// Test routine for the LRUCache class.
public static void main (String[] args) {
   LRUCache c = new LRUCache(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 e : c.getAll())
      System.out.println (e.getKey() + " : " + e.getValue()); }

3，LFU(最近最不常用)

import java.util.*;

public class LFUAgingMap extends HashMap {
    private static final int DEFAULT_MAX_SIZE = 3;
    private int maxSize = DEFAULT_MAX_SIZE;
    Map km = new HashMap();

    public LFUAgingMap() {
        this(DEFAULT_MAX_SIZE);
    }

    public LFUAgingMap(int maxSize) {
        super(maxSize);
        this.maxSize = maxSize;
    }

    @Override
    public V get(Object key) {
        V v = super.get(key);
        if (v != null) {
            HitRate hitRate = km.get(key);
            hitRate.hitCount += 1;
            hitRate.atime = System.nanoTime();
        }
        return v;
    }

    @Override
    public V put(K key, V value) {
        while (km.size() >= maxSize) {
            K k = getLFUAging();
            km.remove(k);
            this.remove(k);
        }
        V v = super.put(key, value);
        km.put(key, new HitRate(key, 1, System.nanoTime()));
        return v;
    }

    private K getLFUAging() {
        HitRate min = Collections.min(km.values());                                  // 使用了排序
        return min.key;
    }

    class HitRate implements Comparable {
        K key;
        Integer hitCount; // 命中次数
        Long atime; // 上次命中时间

        public HitRate(K key, Integer hitCount, Long atime) {
            this.key = key;
            this.hitCount = hitCount;
            this.atime = atime;
        }

        @Override
        public int compareTo(HitRate o) {
            int hr = hitCount.compareTo(o.hitCount);
            return hr != 0 ? hr : atime.compareTo(o.atime);
        }
    }
    public static void main(String[] as) throws Exception {
        LFUAgingMap cache = new LFUAgingMap();
        cache.put("a", "a");
        cache.put("b", "b");
        cache.put("c", "c");

        cache.get("a");
        cache.get("a");

        cache.put("d", "d");
        cache.get("d");
        cache.get("c");
        cache.put("e", "e");

        for (String key : cache.keySet()) {
            System.out.println(key);
        }
    }
}