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
019package org.apache.hadoop.mapred.lib;
020
021import java.io.IOException;
022
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025import org.apache.hadoop.mapred.MapReduceBase;
026import org.apache.hadoop.mapred.Mapper;
027import org.apache.hadoop.mapred.OutputCollector;
028import org.apache.hadoop.mapred.Reporter;
029
030/** 
031 * A {@link Mapper} that swaps keys and values. 
032 */
033@InterfaceAudience.Public
034@InterfaceStability.Stable
035public 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}