cachemanager.java

JSP+Struts+缓存的公司管理系统

//---------------------------------------------------------
// Application: Company Applcation
// Author     : Cao guangxin
// File       : CacheManager.java
//
// Copyright 2006 RelationInfo Software
// Writed at Wed Apr 12 08:58:55 CST 2006
// writed by Eclipse SDK
// Visit http://www.37signals.cn
//---------------------------------------------------------

package net.cn37signals.company.util;

import java.util.Comparator;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.TreeMap;

class CostComparator implements Comparator {
	public int compare(Object o1, Object o2) {
		return ((Double) o1).compareTo((Double) o2);
	}

	public boolean equals(Object o) {
		return super.equals(o);
	}
}

public class CacheManager {
	public static int LRU = 0;

	public static int LFU = 1;

	public static int MIX = 2;

	private HashMap cacheHashMap = new HashMap();

	private int CACHE_CAPACITY = 100;

	private int TRESHOLD = 90;

	private int purgeAlgorithm;

	private long hitCount = 0;

	private long missCount = 0;

	public CacheManager(int purgeAlgorithm, int cacheCapacity, int treshold) {
		this.purgeAlgorithm = purgeAlgorithm;
		CACHE_CAPACITY = cacheCapacity;
		TRESHOLD = treshold;
	}

	public CacheManager(int purgeAlgorithm) {
		this.purgeAlgorithm = purgeAlgorithm;
	}

	public synchronized Object getCache(String identifier) {
		CachedObject cachedObject = (CachedObject) cacheHashMap.get(identifier);
		Object obj = null;

		if (cachedObject == null) {
			missCount++;
		} else if (cachedObject.isExpired()) {
			cacheHashMap.remove(identifier);
			missCount++;
		} else {
			cachedObject.incNumAccess();
			cachedObject.setLastAccessTime(new Date());
			hitCount++;
			obj = cachedObject.getObject();
		}
		return obj;
	}

	public synchronized void invalidate(String identifier) {
		cacheHashMap.remove(identifier);
	}

	public long getHitCount() {
		return hitCount;
	}

	public long getMissCount() {
		return missCount;
	}

	public long getCurrentCacheSize() {
		return cacheHashMap.size();
	}

	public synchronized void putCache(Object object, String id,
			int minutesToLive) {
		CachedObject cachedObject = new CachedObject(object, id, minutesToLive);
		if (cacheHashMap.size() == CACHE_CAPACITY) {
			sweep();
		}
		cacheHashMap.put(id, cachedObject);
	}

	public synchronized void sweep() {
		TreeMap costTreeMap = new TreeMap(new CostComparator());
		for (Iterator i = cacheHashMap.entrySet().iterator(); i.hasNext();) {
			Map.Entry entry = (Map.Entry) i.next();
			CachedObject cachedObject = (CachedObject) entry.getValue();
			if (cachedObject.isExpired()) {
				cacheHashMap.remove(entry.getKey());
			} else {
				double cost = 0.0;
				switch (purgeAlgorithm) {
				case 0:
					cost = cachedObject.getLFUCost();
					break;
				case 1:
					cost = cachedObject.getLRUCost();
					break;
				default:
					cost = cachedObject.getMixCost();
				}
				costTreeMap.put(new Double(cost), entry.getKey());
			}
		}

		// delete to treshold
		for (int i = cacheHashMap.size(); i > TRESHOLD; i--) {
			Object kk = costTreeMap.firstKey();
			Object k = costTreeMap.get(kk);
			cacheHashMap.remove(k);
			costTreeMap.remove(kk);
		}
	}

	public void clearCache() {
		hitCount = 0;
		missCount = 0;
		cacheHashMap.clear();
	}

	public static String createKey(String[] keys) {
		StringBuffer newKey = new StringBuffer("");
		for (int i = 0; i < keys.length; i++)
			newKey.append(keys[i]).append("/");
		return newKey.toString();
	}
}