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.aggregate;
020
021import java.io.IOException;
022import java.util.Iterator;
023import java.util.Map.Entry;
024
025import org.apache.hadoop.classification.InterfaceAudience;
026import org.apache.hadoop.classification.InterfaceStability;
027import org.apache.hadoop.io.Text;
028import org.apache.hadoop.io.Writable;
029import org.apache.hadoop.io.WritableComparable;
030import org.apache.hadoop.mapred.OutputCollector;
031import org.apache.hadoop.mapred.Reporter;
032
033/**
034 * This class implements the generic mapper of Aggregate.
035 */
036@InterfaceAudience.Public
037@InterfaceStability.Stable
038public 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}