LRUCache.java

/*
 * 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.activemq.artemis.selector.impl;

import java.util.LinkedHashMap;
import java.util.Map;

/**
 * A Simple LRU Cache
 *
 * @param <K>
 * @param <V>
 */

public class LRUCache<K, V> extends LinkedHashMap<K, V> {

   private static final long serialVersionUID = -342098639681884413L;
   protected int maxCacheSize = 10000;

   /**
    * Default constructor for an LRU Cache The default capacity is 10000
    */
   public LRUCache() {
      this(0, 10000, 0.75f, true);
   }

   /**
    * Constructs a LRUCache with a maximum capacity
    *
    * @param maximumCacheSize
    */
   public LRUCache(int maximumCacheSize) {
      this(0, maximumCacheSize, 0.75f, true);
   }

   /**
    * Constructs an empty <tt>LRUCache</tt> instance with the specified
    * initial capacity, maximumCacheSize,load factor and ordering mode.
    *
    * @param initialCapacity  the initial capacity.
    * @param maximumCacheSize
    * @param loadFactor       the load factor.
    * @param accessOrder      the ordering mode - <tt>true</tt> for access-order,
    *                         <tt>false</tt> for insertion-order.
    * @throws IllegalArgumentException if the initial capacity is negative or
    *                                  the load factor is non-positive.
    */

   public LRUCache(int initialCapacity, int maximumCacheSize, float loadFactor, boolean accessOrder) {
      super(initialCapacity, loadFactor, accessOrder);
      this.maxCacheSize = maximumCacheSize;
   }

   /**
    * @return Returns the maxCacheSize.
    */
   public int getMaxCacheSize() {
      return maxCacheSize;
   }

   /**
    * @param maxCacheSize The maxCacheSize to set.
    */
   public void setMaxCacheSize(int maxCacheSize) {
      this.maxCacheSize = maxCacheSize;
   }

   @Override
   protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
      if (size() > maxCacheSize) {
         onCacheEviction(eldest);
         return true;
      }
      return false;
   }

   protected void onCacheEviction(Map.Entry<K, V> eldest) {
   }
}