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
024 /**
025 * Aggregate all exchanges into a {@link List} of values defined by the {@link #getValue(Exchange)} call.
026 * The combined Exchange will hold all the aggregated exchanges in a {@link java.util.List}
027 * as a exchange property with the key {@link org.apache.camel.Exchange#GROUPED_EXCHANGE}.
028 * <p/>
029 * The method {@link #isStoreAsBodyOnCompletion()} determines if the aggregated {@link List} should
030 * be stored on the {@link org.apache.camel.Message#setBody(Object)} or be kept as a property
031 * on the exchange.
032 * <br/>
033 * The default behavior to store as message body, allows to more easily group together a list of values
034 * and have its result stored as a {@link List} on the completed {@link Exchange}.
035 *
036 * @since 2.11
037 */
038 public abstract class AbstractListAggregationStrategy<V> implements CompletionAwareAggregationStrategy {
039
040 /**
041 * This method is implemented by the sub-class and is called to retrieve
042 * an instance of the value that will be aggregated and forwarded to the
043 * receiving end point.
044 * <p/>
045 * If <tt>null</tt> is returned, then the value is <b>not</b> added to the {@link List}.
046 *
047 * @param exchange The exchange that is used to retrieve the value from
048 * @return An instance of V that is the associated value of the passed exchange
049 */
050 public abstract V getValue(Exchange exchange);
051
052 /**
053 * Whether to store the completed aggregated {@link List} as message body, or to keep as property on the exchange.
054 * <p/>
055 * The default behavior is <tt>true</tt> to store as message body.
056 *
057 * @return <tt>true</tt> to store as message body, <tt>false</tt> to keep as property on the exchange.
058 */
059 public boolean isStoreAsBodyOnCompletion() {
060 return true;
061 }
062
063 @SuppressWarnings("unchecked")
064 public void onCompletion(Exchange exchange) {
065 if (isStoreAsBodyOnCompletion()) {
066 List<V> list = (List<V>) exchange.removeProperty(Exchange.GROUPED_EXCHANGE);
067 if (list != null) {
068 exchange.getIn().setBody(list);
069 }
070 }
071 }
072
073 /**
074 * This method will aggregate the old and new exchange and return the result.
075 *
076 * @param oldExchange The oldest exchange, can be null
077 * @param newExchange The newest exchange, can be null
078 * @return a composite exchange of the old and/or new exchanges
079 */
080 public Exchange aggregate(Exchange oldExchange, Exchange newExchange) {
081 List<V> list;
082
083 if (oldExchange == null) {
084 list = getList(newExchange);
085 } else {
086 list = getList(oldExchange);
087 }
088
089 if (newExchange != null) {
090 V value = getValue(newExchange);
091 if (value != null) {
092 list.add(value);
093 }
094 }
095
096 return oldExchange != null ? oldExchange : newExchange;
097 }
098
099 @SuppressWarnings("unchecked")
100 private List<V> getList(Exchange exchange) {
101 List<V> list = exchange.getProperty(Exchange.GROUPED_EXCHANGE, List.class);
102 if (list == null) {
103 list = new GroupedExchangeList();
104 exchange.setProperty(Exchange.GROUPED_EXCHANGE, list);
105 }
106 return list;
107 }
108
109 /**
110 * A list to contains grouped {@link Exchange}s.
111 */
112 private static final class GroupedExchangeList extends ArrayList {
113
114 @Override
115 public String toString() {
116 // lets override toString so we don't write data for all the Exchanges by default
117 return "List<Exchange>(" + size() + " elements)";
118 }
119 }
120
121 }