cachemanager.java

本例采用sql server数据库。基于JBuilder的tomcat上运行。访问数据库基于struts的datasources.里面有详细的操作和设置说明。

//---------------------------------------------------------
// Application: Gsm of Application
// Author     : esingle
// File       : CacheManager.java
//
// Copyright 2004 landsoft corp
// Generated at Wed Mar 10 15:35:57 CST 2004
// created by 曹广鑫
// mailto:[e-mail]
//---------------------------------------------------------

package com.landsoft.gsm.util;

import java.util.*;

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 final static int LRU = 0;
  public final static int LFU = 1;
  public final 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 LFU:
            cost = cachedObject.getLFUCost();
            break;
          case LRU:
            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();
  }
}