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;
020import org.slf4j.Logger;
021import org.slf4j.LoggerFactory;
022
023import java.io.IOException;
024import java.util.ArrayList;
025import java.util.HashMap;
026import java.util.Iterator;
027import java.util.LinkedList;
028
029
030/**
031 * An eviction strategy which evicts the oldest message within messages with the same property value
032 *
033 *
034 * @org.apache.xbean.XBean
035 *
036 */
037public class UniquePropertyMessageEvictionStrategy extends MessageEvictionStrategySupport {
038
039    private static final Logger LOG = LoggerFactory.getLogger(UniquePropertyMessageEvictionStrategy.class);
040
041    protected String propertyName;
042
043    public String getPropertyName() {
044        return propertyName;
045    }
046
047    public void setPropertyName(String propertyName) {
048        this.propertyName = propertyName;
049    }
050
051    @Override
052    public MessageReference[] evictMessages(LinkedList messages) throws IOException {
053        MessageReference oldest = (MessageReference)messages.getFirst();
054        HashMap<Object, MessageReference> pivots = new HashMap<Object, MessageReference>();
055        Iterator iter = messages.iterator();
056
057        for (int i = 0; iter.hasNext(); i++) {
058            MessageReference reference = (MessageReference) iter.next();
059            if (propertyName != null && reference.getMessage().getProperty(propertyName) != null) {
060                Object key = reference.getMessage().getProperty(propertyName);
061                if (pivots.containsKey(key)) {
062                    MessageReference pivot = pivots.get(key);
063                    if (reference.getMessage().getTimestamp() > pivot.getMessage().getTimestamp()) {
064                         pivots.put(key, reference);
065                    }
066                } else {
067                    pivots.put(key, reference);
068                }
069            }
070        }
071
072        if (!pivots.isEmpty()) {
073            for (MessageReference ref : pivots.values()) {
074                messages.remove(ref);
075            }
076
077            if (messages.size() != 0) {
078                return (MessageReference[])messages.toArray(new MessageReference[messages.size()]);
079            }
080        }
081        return new MessageReference[] {oldest};
082
083    }
084}