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; 023 024 import org.apache.hadoop.classification.InterfaceAudience; 025 import org.apache.hadoop.classification.InterfaceStability; 026 import org.apache.hadoop.io.Text; 027 import org.apache.hadoop.io.Writable; 028 import org.apache.hadoop.io.WritableComparable; 029 import org.apache.hadoop.mapred.OutputCollector; 030 import org.apache.hadoop.mapred.Reporter; 031 032 /** 033 * This class implements the generic reducer of Aggregate. 034 */ 035 @InterfaceAudience.Public 036 @InterfaceStability.Stable 037 public 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 * @value the values to be aggregated 049 */ 050 public void reduce(Text key, Iterator<Text> values, 051 OutputCollector<Text, Text> output, Reporter reporter) throws IOException { 052 String keyStr = key.toString(); 053 int pos = keyStr.indexOf(ValueAggregatorDescriptor.TYPE_SEPARATOR); 054 String type = keyStr.substring(0, pos); 055 keyStr = keyStr.substring(pos 056 + ValueAggregatorDescriptor.TYPE_SEPARATOR.length()); 057 058 ValueAggregator aggregator = ValueAggregatorBaseDescriptor 059 .generateValueAggregator(type); 060 while (values.hasNext()) { 061 aggregator.addNextValue(values.next()); 062 } 063 064 String val = aggregator.getReport(); 065 key = new Text(keyStr); 066 output.collect(key, new Text(val)); 067 } 068 069 /** 070 * Do nothing. Should not be called 071 */ 072 public void map(K1 arg0, V1 arg1, OutputCollector<Text, Text> arg2, 073 Reporter arg3) throws IOException { 074 throw new IOException ("should not be called\n"); 075 } 076 }