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.commons.collections.functors;
018    
019    import java.io.Serializable;
020    import java.util.Map;
021    
022    import org.apache.commons.collections.Transformer;
023    
024    /**
025     * Transformer implementation that returns the value held in a specified map
026     * using the input parameter as a key.
027     * 
028     * @since Commons Collections 3.0
029     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
030     *
031     * @author Stephen Colebourne
032     */
033    public final class MapTransformer implements Transformer, Serializable {
034    
035        /** Serial version UID */
036        private static final long serialVersionUID = 862391807045468939L;
037        
038        /** The map of data to lookup in */
039        private final Map iMap;
040    
041        /**
042         * Factory to create the transformer.
043         * <p>
044         * If the map is null, a transformer that always returns null is returned.
045         * 
046         * @param map the map, not cloned
047         * @return the transformer
048         */
049        public static Transformer getInstance(Map map) {
050            if (map == null) {
051                return ConstantTransformer.NULL_INSTANCE;
052            }
053            return new MapTransformer(map);
054        }
055    
056        /**
057         * Constructor that performs no validation.
058         * Use <code>getInstance</code> if you want that.
059         * 
060         * @param map  the map to use for lookup, not cloned
061         */
062        private MapTransformer(Map map) {
063            super();
064            iMap = map;
065        }
066    
067        /**
068         * Transforms the input to result by looking it up in a <code>Map</code>.
069         * 
070         * @param input  the input object to transform
071         * @return the transformed result
072         */
073        public Object transform(Object input) {
074            return iMap.get(input);
075        }
076    
077        /**
078         * Gets the map to lookup in.
079         * 
080         * @return the map
081         * @since Commons Collections 3.1
082         */
083        public Map getMap() {
084            return iMap;
085        }
086    
087    }