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;
023
024import org.apache.hadoop.classification.InterfaceAudience;
025import org.apache.hadoop.classification.InterfaceStability;
026import org.apache.hadoop.io.Text;
027import org.apache.hadoop.io.Writable;
028import org.apache.hadoop.io.WritableComparable;
029import org.apache.hadoop.mapred.JobConf;
030import org.apache.hadoop.mapred.OutputCollector;
031import org.apache.hadoop.mapred.Reporter;
032
033/**
034 * This class implements the generic combiner of Aggregate.
035 */
036@InterfaceAudience.Public
037@InterfaceStability.Stable
038public class ValueAggregatorCombiner<K1 extends WritableComparable,
039                                     V1 extends Writable>
040  extends ValueAggregatorJobBase<K1, V1> {
041
042  /**
043   * Combiner does not need to configure.
044   */
045  public void configure(JobConf job) {
046
047  }
048
049  /** Combines values for a given key.  
050   * @param key the key is expected to be a Text object, whose prefix indicates
051   * the type of aggregation to aggregate the values. 
052   * @param values the values to combine
053   * @param output to collect combined values
054   */
055  public void reduce(Text key, Iterator<Text> values,
056                     OutputCollector<Text, Text> output, Reporter reporter) throws IOException {
057    String keyStr = key.toString();
058    int pos = keyStr.indexOf(ValueAggregatorDescriptor.TYPE_SEPARATOR);
059    String type = keyStr.substring(0, pos);
060    ValueAggregator aggregator = ValueAggregatorBaseDescriptor
061      .generateValueAggregator(type);
062    while (values.hasNext()) {
063      aggregator.addNextValue(values.next());
064    }
065    Iterator outputs = aggregator.getCombinerOutput().iterator();
066
067    while (outputs.hasNext()) {
068      Object v = outputs.next();
069      if (v instanceof Text) {
070        output.collect(key, (Text)v);
071      } else {
072        output.collect(key, new Text(v.toString()));
073      }
074    }
075  }
076
077  /** 
078   * Do nothing. 
079   *
080   */
081  public void close() throws IOException {
082
083  }
084
085  /** 
086   * Do nothing. Should not be called. 
087   *
088   */
089  public void map(K1 arg0, V1 arg1, OutputCollector<Text, Text> arg2,
090                  Reporter arg3) throws IOException {
091    throw new IOException ("should not be called\n");
092  }
093}