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     */
017    package org.apache.camel.processor.idempotent;
018    
019    import org.apache.camel.Exchange;
020    import org.apache.camel.Expression;
021    import org.apache.camel.Processor;
022    import org.apache.camel.impl.ServiceSupport;
023    import org.apache.camel.util.ExpressionHelper;
024    import org.apache.camel.util.ServiceHelper;
025    import org.apache.commons.logging.Log;
026    import org.apache.commons.logging.LogFactory;
027    
028    /**
029     * An implementation of the <a
030     * href="http://activemq.apache.org/camel/idempotent-consumer.html">Idempotent
031     * Consumer</a> pattern.
032     * 
033     * @version $Revision: 35332 $
034     */
035    public class IdempotentConsumer extends ServiceSupport implements Processor {
036        private static final transient Log LOG = LogFactory.getLog(IdempotentConsumer.class);
037        private Expression<Exchange> messageIdExpression;
038        private Processor nextProcessor;
039        private MessageIdRepository messageIdRepository;
040    
041        public IdempotentConsumer(Expression<Exchange> messageIdExpression,
042                                  MessageIdRepository messageIdRepository, Processor nextProcessor) {
043            this.messageIdExpression = messageIdExpression;
044            this.messageIdRepository = messageIdRepository;
045            this.nextProcessor = nextProcessor;
046        }
047    
048        @Override
049        public String toString() {
050            return "IdempotentConsumer[expression=" + messageIdExpression + ", repository=" + messageIdRepository
051                   + ", processor=" + nextProcessor + "]";
052        }
053    
054        public void process(Exchange exchange) throws Exception {
055            String messageId = ExpressionHelper.evaluateAsString(messageIdExpression, exchange);
056            if (messageId == null) {
057                throw new NoMessageIdException(exchange, messageIdExpression);
058            }
059            if (!messageIdRepository.contains(messageId)) {
060                nextProcessor.process(exchange);
061            } else {
062                onDuplicateMessage(exchange, messageId);
063            }
064        }
065    
066        // Properties
067        // -------------------------------------------------------------------------
068        public Expression<Exchange> getMessageIdExpression() {
069            return messageIdExpression;
070        }
071    
072        public MessageIdRepository getMessageIdRepository() {
073            return messageIdRepository;
074        }
075    
076        public Processor getNextProcessor() {
077            return nextProcessor;
078        }
079    
080        // Implementation methods
081        // -------------------------------------------------------------------------
082    
083        protected void doStart() throws Exception {
084            ServiceHelper.startServices(nextProcessor);
085        }
086    
087        protected void doStop() throws Exception {
088            ServiceHelper.stopServices(nextProcessor);
089        }
090    
091        /**
092         * A strategy method to allow derived classes to overload the behaviour of
093         * processing a duplicate message
094         * 
095         * @param exchange the exchange
096         * @param messageId the message ID of this exchange
097         */
098        protected void onDuplicateMessage(Exchange exchange, String messageId) {
099            if (LOG.isDebugEnabled()) {
100                LOG.debug("Ignoring duplicate message with id: " + messageId + " for exchange: " + exchange);
101            }
102        }
103    }