| /** |
| * 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.camel.processor.aggregate; |
| |
| import org.apache.camel.Exchange; |
| |
| /** |
| * A strategy for aggregating two exchanges together into a single exchange. |
| * <p/> |
| * On the first invocation of the {@link #aggregate(org.apache.camel.Exchange, org.apache.camel.Exchange) aggregate} |
| * method the <tt>oldExchange</tt> parameter is <tt>null</tt>. The reason is that we have not aggregated anything yet. |
| * So its only the <tt>newExchange</tt> that has a value. Usually you just return the <tt>newExchange</tt> in this |
| * situation. But you still have the power to decide what to do, for example you can do some alternation on the exchange |
| * or remove some headers. And a more common use case is for instance to count some values from the body payload. That |
| * could be to sum up a total amount etc. |
| * <p/> |
| * It is possible that <tt>newExchange</tt> is <tt>null</tt> which could happen if there was no data possible |
| * to acquire. Such as when using a {@link org.apache.camel.processor.PollEnricher} to poll from a JMS queue which |
| * is empty and a timeout was set. |
| * <p/> |
| * Possible implementations include performing some kind of combining or delta processing, such as adding line items |
| * together into an invoice or just using the newest exchange and removing old exchanges such as for state tracking or |
| * market data prices; where old values are of little use. |
| * |
| * @version |
| */ |
| public interface AggregationStrategy { |
| |
| // TODO: In Camel 3.0 we should move this to org.apache.camel package |
| |
| /** |
| * Aggregates an old and new exchange together to create a single combined exchange |
| * |
| * @param oldExchange the oldest exchange (is <tt>null</tt> on first aggregation as we only have the new exchange) |
| * @param newExchange the newest exchange (can be <tt>null</tt> if there was no data possible to acquire) |
| * @return a combined composite of the two exchanges |
| */ |
| Exchange aggregate(Exchange oldExchange, Exchange newExchange); |
| } |