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.broker.region.policy;
018
019import org.apache.activemq.broker.region.MessageReference;
020
021import java.io.IOException;
022import java.util.HashMap;
023import java.util.Iterator;
024import java.util.LinkedList;
025
026
027/**
028 * An eviction strategy which evicts the oldest message within messages with the same property value
029 *
030 *
031 * @org.apache.xbean.XBean
032 *
033 */
034public class UniquePropertyMessageEvictionStrategy extends MessageEvictionStrategySupport {
035
036    protected String propertyName;
037
038    public String getPropertyName() {
039        return propertyName;
040    }
041
042    public void setPropertyName(String propertyName) {
043        this.propertyName = propertyName;
044    }
045
046    @Override
047    public MessageReference[] evictMessages(LinkedList messages) throws IOException {
048        MessageReference oldest = (MessageReference)messages.getFirst();
049        HashMap<Object, MessageReference> pivots = new HashMap<Object, MessageReference>();
050        Iterator iter = messages.iterator();
051
052        for (int i = 0; iter.hasNext(); i++) {
053            MessageReference reference = (MessageReference) iter.next();
054            if (propertyName != null && reference.getMessage().getProperty(propertyName) != null) {
055                Object key = reference.getMessage().getProperty(propertyName);
056                if (pivots.containsKey(key)) {
057                    MessageReference pivot = pivots.get(key);
058                    if (reference.getMessage().getTimestamp() > pivot.getMessage().getTimestamp()) {
059                         pivots.put(key, reference);
060                    }
061                } else {
062                    pivots.put(key, reference);
063                }
064            }
065        }
066
067        if (!pivots.isEmpty()) {
068            for (MessageReference ref : pivots.values()) {
069                messages.remove(ref);
070            }
071
072            if (messages.size() != 0) {
073                return (MessageReference[])messages.toArray(new MessageReference[messages.size()]);
074            }
075        }
076        return new MessageReference[] {oldest};
077
078    }
079}