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.Mapper;
026import org.apache.hadoop.mapred.OutputCollector;
027import org.apache.hadoop.mapred.Reporter;
028import org.apache.hadoop.mapred.MapReduceBase;
029
030/** 
031 * Implements the identity function, mapping inputs directly to outputs. 
032 */
033@InterfaceAudience.Public
034@InterfaceStability.Stable
035public class IdentityMapper<K, V>
036    extends MapReduceBase implements Mapper<K, V, K, V> {
037
038  /** The identity function.  Input key/value pair is written directly to
039   * output.*/
040  public void map(K key, V val,
041                  OutputCollector<K, V> output, Reporter reporter)
042    throws IOException {
043    output.collect(key, val);
044  }
045}