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; 020 021 import java.io.IOException; 022 import java.util.Iterator; 023 024 import org.apache.hadoop.mapred.Reducer; 025 import org.apache.hadoop.mapred.OutputCollector; 026 import org.apache.hadoop.mapred.Reporter; 027 import org.apache.hadoop.mapred.MapReduceBase; 028 029 import org.apache.hadoop.classification.InterfaceAudience; 030 import org.apache.hadoop.classification.InterfaceStability; 031 import org.apache.hadoop.io.LongWritable; 032 033 /** 034 * A {@link Reducer} that sums long values. 035 */ 036 @InterfaceAudience.Public 037 @InterfaceStability.Stable 038 public class LongSumReducer<K> extends MapReduceBase 039 implements Reducer<K, LongWritable, K, LongWritable> { 040 041 public void reduce(K key, Iterator<LongWritable> values, 042 OutputCollector<K, LongWritable> output, 043 Reporter reporter) 044 throws IOException { 045 046 // sum all values for this key 047 long sum = 0; 048 while (values.hasNext()) { 049 sum += values.next().get(); 050 } 051 052 // output sum 053 output.collect(key, new LongWritable(sum)); 054 } 055 056 }