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.OutputCollector; 030import org.apache.hadoop.mapred.Reporter; 031 032/** 033 * This class implements the generic reducer of Aggregate. 034 */ 035@InterfaceAudience.Public 036@InterfaceStability.Stable 037public class ValueAggregatorReducer<K1 extends WritableComparable, 038 V1 extends Writable> 039 extends ValueAggregatorJobBase<K1, V1> { 040 041 /** 042 * @param key 043 * the key is expected to be a Text object, whose prefix indicates 044 * the type of aggregation to aggregate the values. In effect, data 045 * driven computing is achieved. It is assumed that each aggregator's 046 * getReport method emits appropriate output for the aggregator. This 047 * may be further customiized. 048 * @param values 049 * the values to be aggregated 050 */ 051 public void reduce(Text key, Iterator<Text> values, 052 OutputCollector<Text, Text> output, Reporter reporter) throws IOException { 053 String keyStr = key.toString(); 054 int pos = keyStr.indexOf(ValueAggregatorDescriptor.TYPE_SEPARATOR); 055 String type = keyStr.substring(0, pos); 056 keyStr = keyStr.substring(pos 057 + ValueAggregatorDescriptor.TYPE_SEPARATOR.length()); 058 059 ValueAggregator aggregator = ValueAggregatorBaseDescriptor 060 .generateValueAggregator(type); 061 while (values.hasNext()) { 062 aggregator.addNextValue(values.next()); 063 } 064 065 String val = aggregator.getReport(); 066 key = new Text(keyStr); 067 output.collect(key, new Text(val)); 068 } 069 070 /** 071 * Do nothing. Should not be called 072 */ 073 public void map(K1 arg0, V1 arg1, OutputCollector<Text, Text> arg2, 074 Reporter arg3) throws IOException { 075 throw new IOException ("should not be called\n"); 076 } 077}