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.mapreduce.lib.aggregate;
020    
021    import java.io.IOException;
022    import java.util.Iterator;
023    import java.util.Map.Entry;
024    
025    import org.apache.hadoop.classification.InterfaceAudience;
026    import org.apache.hadoop.classification.InterfaceStability;
027    import org.apache.hadoop.io.Text;
028    import org.apache.hadoop.io.Writable;
029    import org.apache.hadoop.io.WritableComparable;
030    import org.apache.hadoop.mapreduce.Mapper;
031    
032    /**
033     * This class implements the generic mapper of Aggregate.
034     */
035    @InterfaceAudience.Public
036    @InterfaceStability.Stable
037    public class ValueAggregatorMapper<K1 extends WritableComparable<?>,
038                                       V1 extends Writable>
039      extends Mapper<K1, V1, Text, Text> {
040    
041      public void setup(Context context) 
042          throws IOException, InterruptedException {
043        ValueAggregatorJobBase.setup(context.getConfiguration());
044      }
045      
046      /**
047       *  the map function. It iterates through the value aggregator descriptor 
048       *  list to generate aggregation id/value pairs and emit them.
049       */
050      public void map(K1 key, V1 value,
051          Context context) throws IOException, InterruptedException  {
052    
053        Iterator<?> iter = 
054          ValueAggregatorJobBase.aggregatorDescriptorList.iterator();
055        while (iter.hasNext()) {
056          ValueAggregatorDescriptor ad = (ValueAggregatorDescriptor) iter.next();
057          Iterator<Entry<Text, Text>> ens =
058            ad.generateKeyValPairs(key, value).iterator();
059          while (ens.hasNext()) {
060            Entry<Text, Text> en = ens.next();
061            context.write(en.getKey(), en.getValue());
062          }
063        }
064      }
065    }