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 /** 022 * A strategy for aggregating two exchanges together into a single exchange. 023 * <p/> 024 * On the first invocation of the {@link #aggregate(org.apache.camel.Exchange, org.apache.camel.Exchange) aggregate} 025 * method the <tt>oldExchange</tt> parameter is <tt>null</tt>. The reason is that we have not aggregated anything yet. 026 * So its only the <tt>newExchange</tt> that has a value. Usually you just return the <tt>newExchange</tt> in this 027 * situation. But you still have the power to decide what to do, for example you can do some alternation on the exchange 028 * or remove some headers. And a more common use case is for instance to count some values from the body payload. That 029 * could be to sum up a total amount etc. 030 * <p/> 031 * Possible implementations include performing some kind of combining or delta 032 * processing, such as adding line items together into an invoice or just using 033 * the newest exchange and removing old exchanges such as for state tracking or 034 * market data prices; where old values are of little use. 035 * 036 * @version $Revision: 777874 $ 037 */ 038 public interface AggregationStrategy { 039 040 /** 041 * Aggregates an old and new exchange together to create a single combined exchange 042 * 043 * @param oldExchange the oldest exchange (is <tt>null</tt> on first aggregation as we only have the new exchange) 044 * @param newExchange the newest exchange 045 * @return a combined composite of the two exchanges 046 */ 047 Exchange aggregate(Exchange oldExchange, Exchange newExchange); 048 }