cvs commit: jakarta-tomcat/src/share/org/apache/tomcat/util LRUCache.java

[na...@locus.apache.org]

nacho       00/08/12 19:09:34

  Added:       src/share/org/apache/tomcat/util LRUCache.java
  Log:
  Generic LRU Cache class
  
  Revision  Changes    Path
  1.1                  jakarta-tomcat/src/share/org/apache/tomcat/util/LRUCache.java
  
  Index: LRUCache.java
  ===================================================================
  /*
   * $Header: /home/cvs/jakarta-tomcat/src/share/org/apache/tomcat/util/LRUCache.java,v 1.1 2000/08/13 02:09:34 nacho Exp $
   * $Revision: 1.1 $
   * $Date: 2000/08/13 02:09:34 $
   *
   * ====================================================================
   *
   * The Apache Software License, Version 1.1
   *
   * Copyright (c) 1999 The Apache Software Foundation.  All rights 
   * reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer. 
   *
   * 2. 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.
   *
   * 3. The end-user documentation included with the redistribution, if
   *    any, must include the following acknowlegement:  
   *       "This product includes software developed by the 
   *        Apache Software Foundation (http://www.apache.org/)."
   *    Alternately, this acknowlegement may appear in the software itself,
   *    if and wherever such third-party acknowlegements normally appear.
   *
   * 4. The names "The Jakarta Project", "Tomcat", and "Apache Software
   *    Foundation" must not be used to endorse or promote products derived
   *    from this software without prior written permission. For written 
   *    permission, please contact apache@apache.org.
   *
   * 5. Products derived from this software may not be called "Apache"
   *    nor may "Apache" appear in their names without prior written
   *    permission of the Apache Group.
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED 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 APACHE SOFTWARE FOUNDATION OR
   * ITS 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   * [Additional notices, if required by prior licensing conditions]
   *
   */ 
  
   
  package org.apache.tomcat.util;
  
  import java.util.Hashtable;
  
  /**
   * This class implements a Generic LRU Cache
   *
   *
   * @author Ignacio J. Ortega
   *
   */
  
  public class LRUCache
  {
      class CacheNode
      {
  
          CacheNode prev;
          CacheNode next;
          Object value;
          Object key;
  
          CacheNode()
          {
          }
      }
  
  
      public LRUCache(int i)
      {
          currentSize = 0;
          cacheSize = i;
      }
  
      public Object get(Object key)
      {
          if(nodes == null)
              return null;
          CacheNode node = (CacheNode)nodes.get(key);
          if(node != null)
          {
              moveToHead(node);
              return node.value;
          }
          else
          {
              return null;
          }
      }
  
      public void put(Object key, Object value)
      {
          if(nodes == null)
              nodes = new Hashtable(cacheSize);
          CacheNode node = (CacheNode)nodes.get(key);
          if(node == null)
          {
              if(currentSize >= cacheSize)
              {
                  if(last != null)
                      nodes.remove(last.key);
                  removeLast();
              }
              else
              {
                  currentSize++;
              }
              node = new CacheNode();
          }
          node.value = value;
          node.key = key;
          moveToHead(node);
          nodes.put(key, node);
      }
  
      public void clear()
      {
          if(nodes != null)
              nodes.clear();
          first = null;
          last = null;
      }
  
      private void removeLast()
      {
          if(last != null)
          {
              if(last.prev != null)
                  last.prev.next = null;
              else
                  first = null;
              last = last.prev;
          }
      }
  
      private void moveToHead(CacheNode node)
      {
          if(node == first)
              return;
          if(node.prev != null)
              node.prev.next = node.next;
          if(node.next != null)
              node.next.prev = node.prev;
          if(last == node)
              last = node.prev;
          if(first != null)
          {
              node.next = first;
              first.prev = node;
          }
          first = node;
          node.prev = null;
          if(last == null)
              last = first;
      }
  
      private int cacheSize;
      private Hashtable nodes;
      private int currentSize;
      private CacheNode first;
      private CacheNode last;
  }