001 /**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements. See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership. The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with 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
019 package org.apache.hadoop.mapred.lib;
020
021 import java.io.IOException;
022
023 import org.apache.hadoop.classification.InterfaceAudience;
024 import org.apache.hadoop.classification.InterfaceStability;
025 import org.apache.hadoop.mapred.MapReduceBase;
026 import org.apache.hadoop.mapred.Mapper;
027 import org.apache.hadoop.mapred.OutputCollector;
028 import org.apache.hadoop.mapred.Reporter;
029
030 /**
031 * A {@link Mapper} that swaps keys and values.
032 */
033 @InterfaceAudience.Public
034 @InterfaceStability.Stable
035 public class InverseMapper<K, V>
036 extends MapReduceBase implements Mapper<K, V, V, K> {
037
038 /** The inverse function. Input keys and values are swapped.*/
039 public void map(K key, V value,
040 OutputCollector<V, K> output, Reporter reporter)
041 throws IOException {
042 output.collect(value, key);
043 }
044
045 }