001    /**
002     *
003     * Licensed to the Apache Software Foundation (ASF) under one or more
004     * contributor license agreements.  See the NOTICE file distributed with
005     * this work for additional information regarding copyright ownership.
006     * The ASF licenses this file to You under the Apache License, Version 2.0
007     * (the "License"); you may not use this file except in compliance with
008     * the License.  You may obtain a copy of the License at
009     *
010     * http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.camel.util;
019    
020    import java.util.ArrayList;
021    import java.util.List;
022    import java.util.Map;
023    
024    /**
025     * A number of helper methods for working with collections
026     *
027     * @version $Revision: 1.1 $
028     */
029    public class CollectionHelper {
030        /**
031         * Sets the value of the entry in the map for the given key, though if the map already contains a value for the
032         * given key then the value is appended to a list of values.
033         *
034         * @param map   the map to add the entry to
035         * @param key   the key in the map
036         * @param value the value to put in the map
037         */
038        public static void appendValue(Map map, Object key, Object value) {
039    
040            Object oldValue = map.get(key);
041            if (oldValue != null) {
042                List list;
043                if (oldValue instanceof List) {
044                    list = (List) oldValue;
045                }
046                else {
047                    list = new ArrayList();
048                    list.add(oldValue);
049                }
050                list.add(value);
051            }
052            else {
053                map.put(key, value);
054            }
055        }
056    }