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 java.util.ArrayList;
020 import java.util.List;
021
022 import org.apache.camel.Exchange;
023 import org.apache.camel.impl.DefaultExchange;
024
025 /**
026 * Aggregate all exchanges into a {@link List} of values defined by the {@link #getValue(Exchange)} call.
027 * The combined Exchange will hold all the aggregated exchanges in a {@link java.util.List}
028 * as a exchange property with the key {@link org.apache.camel.Exchange#GROUPED_EXCHANGE}.
029 * <p/>
030 * The method {@link #isStoreAsBodyOnCompletion()} determines if the aggregated {@link List} should
031 * be stored on the {@link org.apache.camel.Message#setBody(Object)} or be kept as a property
032 * on the exchange.
033 * <br/>
034 * The default behavior to store as message body, allows to more easily group together a list of values
035 * and have its result stored as a {@link List} on the completed {@link Exchange}.
036 *
037 * @since 2.11
038 */
039 public abstract class AbstractListAggregationStrategy<V> implements CompletionAwareAggregationStrategy {
040
041 /**
042 * This method is implemented by the sub-class and is called to retrieve
043 * an instance of the value that will be aggregated and forwarded to the
044 * receiving end point.
045 * <p/>
046 * If <tt>null</tt> is returned, then the value is <b>not</b> added to the {@link List}.
047 *
048 * @param exchange The exchange that is used to retrieve the value from
049 * @return An instance of V that is the associated value of the passed exchange
050 */
051 public abstract V getValue(Exchange exchange);
052
053 /**
054 * Whether to store the completed aggregated {@link List} as message body, or to keep as property on the exchange.
055 * <p/>
056 * The default behavior is <tt>true</tt> to store as message body.
057 *
058 * @return <tt>true</tt> to store as message body, <tt>false</tt> to keep as property on the exchange.
059 */
060 public boolean isStoreAsBodyOnCompletion() {
061 return true;
062 }
063
064 @SuppressWarnings("unchecked")
065 public void onCompletion(Exchange exchange) {
066 if (isStoreAsBodyOnCompletion()) {
067 List<V> list = (List<V>) exchange.removeProperty(Exchange.GROUPED_EXCHANGE);
068 if (list != null) {
069 exchange.getIn().setBody(list);
070 }
071 }
072 }
073
074 /**
075 * This method will aggregate the old and new exchange and return the result.
076 *
077 * @param oldExchange The oldest exchange, can be null
078 * @param newExchange The newest exchange, can be null
079 * @return a composite exchange of the old and/or new exchanges
080 */
081 public Exchange aggregate(Exchange oldExchange, Exchange newExchange) {
082 List<V> list;
083
084 if (oldExchange == null) {
085 list = getList(newExchange);
086 } else {
087 list = getList(oldExchange);
088 }
089
090 if (newExchange != null) {
091 V value = getValue(newExchange);
092 if (value != null) {
093 list.add(value);
094 }
095 }
096
097 return oldExchange != null ? oldExchange : newExchange;
098 }
099
100 @SuppressWarnings("unchecked")
101 private List<V> getList(Exchange exchange) {
102 List<V> list = exchange.getProperty(Exchange.GROUPED_EXCHANGE, List.class);
103 if (list == null) {
104 list = new ArrayList<V>();
105 exchange.setProperty(Exchange.GROUPED_EXCHANGE, list);
106 }
107 return list;
108 }
109
110 }