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.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.mapred.OutputCollector;
031    import org.apache.hadoop.mapred.Reporter;
032    
033    /**
034     * This class implements the generic mapper of Aggregate.
035     */
036    @InterfaceAudience.Public
037    @InterfaceStability.Stable
038    public class ValueAggregatorMapper<K1 extends WritableComparable,
039                                       V1 extends Writable>
040      extends ValueAggregatorJobBase<K1, V1> {
041    
042      /**
043       *  the map function. It iterates through the value aggregator descriptor 
044       *  list to generate aggregation id/value pairs and emit them.
045       */
046      public void map(K1 key, V1 value,
047                      OutputCollector<Text, Text> output, Reporter reporter) throws IOException {
048    
049        Iterator iter = this.aggregatorDescriptorList.iterator();
050        while (iter.hasNext()) {
051          ValueAggregatorDescriptor ad = (ValueAggregatorDescriptor) iter.next();
052          Iterator<Entry<Text, Text>> ens =
053            ad.generateKeyValPairs(key, value).iterator();
054          while (ens.hasNext()) {
055            Entry<Text, Text> en = ens.next();
056            output.collect(en.getKey(), en.getValue());
057          }
058        }
059      }
060    
061      /**
062       * Do nothing. Should not be called.
063       */
064      public void reduce(Text arg0, Iterator<Text> arg1,
065                         OutputCollector<Text, Text> arg2,
066                         Reporter arg3) throws IOException {
067        throw new IOException("should not be called\n");
068      }
069    }