| /* |
| * Copyright 1999-2004 The Apache Software Foundation |
| * |
| * Licensed 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; |
| } |