LRUCache.java

package com.hphoto.server;

import java.io.Serializable;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

public class LRUCache<K extends Comparable, V> implements Cache<K, V>,Serializable {
	
	private static final long serialVersionUID = 3674312987828041877L;
	Map<K, Item> m_map = Collections.synchronizedMap(new HashMap<K, Item>());
	Item m_start = new Item();
	Item m_end = new Item();
	int m_maxSize;
	Object m_listLock = new Object();
	
	static class Item {
		public Item(Comparable k, Object v, long e) {
		   key = k;
		   value = v;
		   expires = e;
		}
		public Item() {}
		public Comparable key;
		public Object value;
		public long expires;
		public Item previous;
		public Item next;
	}
	
	void removeItem(Item item) {
		synchronized(m_listLock) {
		   item.previous.next = item.next;
		   item.next.previous = item.previous;
		}
	}
	
	void insertHead(Item item) {
		synchronized(m_listLock) {
		   item.previous = m_start;
		   item.next = m_start.next;
		   m_start.next.previous = item;
		   m_start.next = item;
		}
	}
	
	void moveToHead(Item item) {
		synchronized(m_listLock) {
		   item.previous.next = item.next;
		   item.next.previous = item.previous;
		   item.previous = m_start;
		   item.next = m_start.next;
		   m_start.next.previous = item;
		   m_start.next = item;
		}
	}
	public LRUCache(int maxObjects) {
		m_maxSize = maxObjects;
		m_start.next = m_end;
		m_end.previous = m_start;
	}
	
	@SuppressWarnings("unchecked")
	public Pair[] getAll() {
		Pair p[] = new Pair[m_maxSize];
		int count = 0;
		synchronized(m_listLock) {
		   Item cur = m_start.next;
		   while(cur!=m_end) {
		      p[count] = new Pair(cur.key, cur.value);
		      ++count;
		      cur = cur.next;
		   }
		}
		Pair np[] = new Pair[count];
		System.arraycopy(p, 0, np, 0, count);
		return np;
	}
	
	@SuppressWarnings("unchecked")
	public V get(K key) {
		Item cur = m_map.get(key);
		if(cur==null) {
		   return null;
		}
		if(System.currentTimeMillis()>cur.expires) {
		   m_map.remove(cur.key);
		   removeItem(cur);
		   return null;
		}
		if(cur!=m_start.next) {
		   moveToHead(cur);
		}
		return (V)cur.value;
	}
	
	public void put(K key, V obj) {
		put(key, obj, -1);
	}
	
	public void put(K key, V value, long validTime) {
		Item cur = m_map.get(key);
		if(cur!=null) {
		   cur.value = value;
		   if(validTime>0) {
		      cur.expires = System.currentTimeMillis()+validTime;
		   }
		   else {
		      cur.expires = Long.MAX_VALUE;
		   }
		   moveToHead(cur);
		   return;
		}
		if(m_map.size()>=m_maxSize) {
		   cur = m_end.previous;
		   m_map.remove(cur.key);
		   removeItem(cur);
		}
		long expires=0;
		if(validTime>0) {
		   expires = System.currentTimeMillis()+validTime;
		}
		else {
		   expires = Long.MAX_VALUE;
		}
		Item item = new Item(key, value, expires);
		insertHead(item);
		m_map.put(key, item);
	}
	
	public void remove(K key) {
		Item cur = m_map.get(key);
		if(cur==null) {
		   return;
		}
		m_map.remove(key);
		removeItem(cur);
	}
	
	public int size() {
		return m_map.size();
	}
}