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<K,V> extends LinkedHashMap<K, V>{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<K, V> 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 <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>* This class is thread-safe. All methods of this class are synchronized.** <p>* Author: Christian d'Heureuse, Inventec Informatik AG, Zurich, Switzerland<br>* Multi-licensed: EPL / LGPL / GPL / AL / BSD.*/public class LRUCache<K,V> {private static final float   hashTableLoadFactor = 0.75f;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 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 <code>Collection</code> that contains a copy of all cache entries.* @return a <code>Collection</code> with a copy of the cache content.*/public synchronized Collection<Map.Entry<K,V>> getAll() {   return new ArrayList<Map.Entry<K,V>>(map.entrySet()); }} // end class LRUCache------------------------------------------------------------------------------------------// Test routine for the LRUCache class.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()); }

3，LFU(最近最不常用)

import java.util.*;public class LFUAgingMap<K, V> extends HashMap<K, V> {    private static final int DEFAULT_MAX_SIZE = 3;    private int maxSize = DEFAULT_MAX_SIZE;    Map<K, HitRate> km = new HashMap<K, HitRate>();    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<HitRate> {        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<String, String> cache = new LFUAgingMap<String, String>();        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);        }    }}