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.Mapper;
026    import org.apache.hadoop.mapred.OutputCollector;
027    import org.apache.hadoop.mapred.Reporter;
028    import org.apache.hadoop.mapred.MapReduceBase;
029    
030    /** 
031     * Implements the identity function, mapping inputs directly to outputs. 
032     */
033    @InterfaceAudience.Public
034    @InterfaceStability.Stable
035    public class IdentityMapper<K, V>
036        extends MapReduceBase implements Mapper<K, V, K, V> {
037    
038      /** The identify 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    }