Tomcat example source code file (LRUCache.java)

This example Tomcat source code file (LRUCache.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Tomcat tags/keywords

cachenode, cachenode, hashtable, hashtable, lrucache, lrucache, object, object, util

The Tomcat LRUCache.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package org.apache.tomcat.util.collections;

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;
        nodes = new Hashtable(i);
    }

    public Object get(Object key)
    {
        CacheNode node = (CacheNode)nodes.get(key);
        if(node != null)
        {
            moveToHead(node);
            return node.value;
        }
        else
        {
            return null;
        }
    }

    public void put(Object key, Object value)
    {
        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 Object remove(Object key) {
        CacheNode node = (CacheNode)nodes.get(key);
        if (node != null) {
            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 == node)
                first = node.next;
        }
        return node;
    }

    public void 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;
}