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.aggregate;
018    
019    import org.apache.camel.Exchange;
020    
021    import static org.apache.camel.util.ExchangeHelper.hasExceptionBeenHandledByErrorHandler;
022    
023    /**
024     * An {@link AggregationStrategy} which just uses the latest exchange which is useful
025     * for status messages where old status messages have no real value. Another example is things
026     * like market data prices, where old stock prices are not that relevant, only the current price is.
027     *
028     * @version 
029     */
030    public class UseLatestAggregationStrategy implements AggregationStrategy {
031    
032        public Exchange aggregate(Exchange oldExchange, Exchange newExchange) {
033            if (newExchange == null) {
034                return oldExchange;
035            }
036            if (oldExchange == null) {
037                return newExchange;
038            }
039    
040            Exchange answer = null;
041    
042            // propagate exception first
043            propagateException(oldExchange, newExchange);
044            if (newExchange.getException() != null) {
045                answer = newExchange;
046            }
047    
048            if (answer == null) {
049                // the propagate failures
050                answer = propagateFailure(oldExchange, newExchange);
051            }
052    
053            return answer;
054        }
055        
056        protected void propagateException(Exchange oldExchange, Exchange newExchange) {
057            if (oldExchange == null) {
058                return;
059            }
060    
061            // propagate exception from old exchange if there isn't already an exception
062            if (newExchange.getException() == null) {
063                newExchange.setException(oldExchange.getException());
064                newExchange.setProperty(Exchange.FAILURE_ENDPOINT, oldExchange.getProperty(Exchange.FAILURE_ENDPOINT));
065            }
066        }
067    
068        protected Exchange propagateFailure(Exchange oldExchange, Exchange newExchange) {
069            if (oldExchange == null) {
070                return newExchange;
071            }
072    
073            // propagate exception from old exchange if there isn't already an exception
074            boolean exceptionHandled = hasExceptionBeenHandledByErrorHandler(oldExchange);
075            if (oldExchange.isFailed() || oldExchange.isRollbackOnly() || exceptionHandled) {
076                // propagate failure by using old exchange as the answer
077                return oldExchange;
078            }
079    
080            return newExchange;
081        }
082    
083        @Override
084        public String toString() {
085            return "UseLatestAggregationStrategy";
086        }
087    }