001/** 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.activemq.util; 018 019import java.util.LinkedHashMap; 020import java.util.Map; 021 022/** 023 * A Simple LRU Cache 024 * 025 * 026 * @param <K> 027 * @param <V> 028 */ 029 030public class LRUCache<K, V> extends LinkedHashMap<K, V> { 031 private static final long serialVersionUID = -342098639681884413L; 032 protected int maxCacheSize = 10000; 033 034 /** 035 * Default constructor for an LRU Cache The default capacity is 10000 036 */ 037 public LRUCache() { 038 this(0,10000, 0.75f, true); 039 } 040 041 /** 042 * Constructs a LRUCache with a maximum capacity 043 * 044 * @param maximumCacheSize 045 */ 046 public LRUCache(int maximumCacheSize) { 047 this(0, maximumCacheSize, 0.75f, true); 048 } 049 050 /** 051 * Constructs an empty <tt>LRUCache</tt> instance with the specified 052 * initial capacity, maximumCacheSize,load factor and ordering mode. 053 * 054 * @param initialCapacity the initial capacity. 055 * @param maximumCacheSize 056 * @param loadFactor the load factor. 057 * @param accessOrder the ordering mode - <tt>true</tt> for access-order, 058 * <tt>false</tt> for insertion-order. 059 * @throws IllegalArgumentException if the initial capacity is negative or 060 * the load factor is non-positive. 061 */ 062 063 public LRUCache(int initialCapacity, int maximumCacheSize, float loadFactor, boolean accessOrder) { 064 super(initialCapacity, loadFactor, accessOrder); 065 this.maxCacheSize = maximumCacheSize; 066 } 067 068 /** 069 * @return Returns the maxCacheSize. 070 */ 071 public int getMaxCacheSize() { 072 return maxCacheSize; 073 } 074 075 /** 076 * @param maxCacheSize The maxCacheSize to set. 077 */ 078 public void setMaxCacheSize(int maxCacheSize) { 079 this.maxCacheSize = maxCacheSize; 080 } 081 082 protected boolean removeEldestEntry(Map.Entry<K,V> eldest) { 083 if( size() > maxCacheSize ) { 084 onCacheEviction(eldest); 085 return true; 086 } 087 return false; 088 } 089 090 protected void onCacheEviction(Map.Entry<K,V> eldest) { 091 } 092 093}