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The ActiveMQ Message Broker implementation

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/**
 * 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.broker.region.policy;

import java.util.ArrayList;
import java.util.List;
import org.apache.activemq.broker.Broker;
import org.apache.activemq.broker.ConnectionContext;
import org.apache.activemq.broker.region.MessageReference;
import org.apache.activemq.broker.region.SubscriptionRecovery;
import org.apache.activemq.broker.region.Topic;
import org.apache.activemq.command.ActiveMQDestination;
import org.apache.activemq.command.Message;
import org.apache.activemq.filter.DestinationFilter;

/**
 * This implementation of {@link SubscriptionRecoveryPolicy} will only keep the
 * last message.
 * 
 * @org.apache.xbean.XBean
 * 
 */
public class LastImageSubscriptionRecoveryPolicy implements SubscriptionRecoveryPolicy {

    private volatile MessageReference lastImage;

    public boolean add(ConnectionContext context, MessageReference node) throws Exception {
        lastImage = node;
        return true;
    }

    public void recover(ConnectionContext context, Topic topic, SubscriptionRecovery sub) throws Exception {
        // Re-dispatch the last message seen.
        MessageReference node = lastImage;
        if (node != null) {
            sub.addRecoveredMessage(context, node);
        }
    }

    public void start() throws Exception {
    }

    public void stop() throws Exception {
    }

    public Message[] browse(ActiveMQDestination destination) throws Exception {
        List result = new ArrayList();
        if (lastImage != null) {
            DestinationFilter filter = DestinationFilter.parseFilter(destination);
            if (filter.matches(lastImage.getMessage().getDestination())) {
                result.add(lastImage.getMessage());
            }
        }
        return result.toArray(new Message[result.size()]);
    }

    public SubscriptionRecoveryPolicy copy() {
        return new LastImageSubscriptionRecoveryPolicy();
    }
    
    public void setBroker(Broker broker) {        
    }

}