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.util;
018    
019    import java.util.ArrayList;
020    import java.util.List;
021    import java.util.Map;
022    
023    /**
024     * A number of helper methods for working with collections
025     * 
026     * @version $Revision: 1.1 $
027     */
028    public class CollectionHelper {
029        
030        /**
031         * Utility classes should not have a public constructor.
032         */
033        private CollectionHelper() {        
034        }
035        
036        /**
037         * Sets the value of the entry in the map for the given key, though if the
038         * map already contains a value for the given key then the value is appended
039         * to a list of values.
040         * 
041         * @param map the map to add the entry to
042         * @param key the key in the map
043         * @param value the value to put in the map
044         */
045        public static void appendValue(Map map, Object key, Object value) {
046    
047            Object oldValue = map.get(key);
048            if (oldValue != null) {
049                List list;
050                if (oldValue instanceof List) {
051                    list = (List)oldValue;
052                } else {
053                    list = new ArrayList();
054                    list.add(oldValue);
055                }
056                list.add(value);
057            } else {
058                map.put(key, value);
059            }
060        }
061    }