cache.java

一个工作流设计及定义的系统,可以直接与数据库结合进行系统工作流程的定义及应用.

/*
 * Copyright (c) 2005, John Mettraux, OpenWFE.org
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 * 
 * . Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.  
 * 
 * . Redistributions in binary form must reproduce the above copyright notice, 
 *   this list of conditions and the following disclaimer in the documentation 
 *   and/or other materials provided with the distribution.
 * 
 * . Neither the name of the "OpenWFE" nor the names of its contributors may be
 *   used to endorse or promote products derived from this software without
 *   specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * $Id: Cache.java,v 1.15 2005/05/17 16:40:12 jmettraux Exp $
 */

//
// Cache.java
//
// [e-mail]
//
// generated with 
// jtmpl 1.0.04 20.11.2001 John Mettraux ([e-mail])
//

package openwfe.org;

import openwfe.org.xml.XmlUtils;


/**
 * A cache implementation : it's in fact a map with a max capacity.
 * When you put an item in a cache that is full, the least recently used item
 * will be thrown out to give its place to the incoming item.
 *
 * <p><font size=2>CVS Info :
 * <br>$Author: jmettraux $
 * <br>$Date: 2005/05/17 16:40:12 $
 * <br>$Id: Cache.java,v 1.15 2005/05/17 16:40:12 jmettraux Exp $ </font>
 *
 * @author [e-mail]
 */
public class Cache
{

    /*
    private final static org.apache.log4j.Logger log = org.apache.log4j.Logger
        .getLogger(Cache.class.getName());
    */

    //
    // FIELDS

    private java.util.Map cache = new java.util.HashMap();
    private java.util.List lru = new java.util.ArrayList(0);

    private int maxSize = 100;

    //
    // CONSTRUCTORS

    /**
     * Builds a cache with a custom maxSize.
     */
    public Cache (final int maxSize)
    {
        super();

        if (maxSize < 1) 
        {
            throw new IllegalArgumentException
                ("Cannot build a cache with a maxSize < 1 : "+maxSize);
        }

        this.maxSize = maxSize;
    }

    /**
     * Builds a cache with the default capacity (maxSize set to 100).
     */
    public Cache ()
    {
        super();
    }

    //
    // METHODS

    /**
     * Like the get() method of a Map.
     */
    public synchronized Object get (final Object key)
    {
        Object result = this.cache.get(key);

        if (result != null)
        {
            if (this.lru.contains(key)) this.lru.remove(key);
            this.lru.add(0, key);
        }

        adjust();

        return result;
    }

    /**
     * Like the remove() method of a Map.
     */
    public synchronized void remove (final Object key)
    {
        this.cache.remove(key);
        this.lru.remove(key);
    }

    /**
     * Like the put() method of a Map.
     */
    public synchronized void put (final Object key, final Object value)
    {
        this.cache.put(key, value);
        this.lru.add(0, key);
        adjust();
    }

    private void adjust()
    {
        while (this.lru.size() > maxSize)
        {
            Object key = this.lru.remove(this.lru.size()-1);
            this.cache.remove(key);
        }
    }

    /**
     * Returns the count of items currently stored in this cache.
     */
    public int size ()
    {
        return this.cache.size();
    }

    /**
     * Returns the capacity attributed to this cache.
     */
    public int getMaxSize ()
    {
        return this.maxSize;
    }

    /**
     * Beware : you have to handle sync by yourself
     */
    public java.util.Iterator iterator ()
    {
        return this.cache.values().iterator();
    }

    /**
     * Like the keySet() method of a Map.
     */
    public java.util.Set keySet ()
    {
        return this.cache.keySet();
    }

    /**
     * This method is used by the getStatus() method of services 
     * using a cache
     */
    public org.jdom.Element getStatus ()
    {
        org.jdom.Element cacheElt = new org.jdom.Element("cache");

        cacheElt.addContent(XmlUtils.getRevisionElt("$Id: Cache.java,v 1.15 2005/05/17 16:40:12 jmettraux Exp $"));

        java.util.Iterator it = this.cache.keySet().iterator();
        while (it.hasNext())
        {
            org.jdom.Element keyElt = new org.jdom.Element("key");
            keyElt.addContent(it.next().toString());
            cacheElt.addContent(keyElt);
        }

        return cacheElt;
    }

}