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}