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.mapreduce.lib.reduce;
020    
021    import java.io.IOException;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import org.apache.hadoop.classification.InterfaceStability;
025    import org.apache.hadoop.io.LongWritable;
026    import org.apache.hadoop.mapreduce.Reducer;
027    
028    @InterfaceAudience.Public
029    @InterfaceStability.Stable
030    public class LongSumReducer<KEY> extends Reducer<KEY, LongWritable,
031                                                     KEY,LongWritable> {
032    
033      private LongWritable result = new LongWritable();
034    
035      public void reduce(KEY key, Iterable<LongWritable> values,
036                         Context context) throws IOException, InterruptedException {
037        long sum = 0;
038        for (LongWritable val : values) {
039          sum += val.get();
040        }
041        result.set(sum);
042        context.write(key, result);
043      }
044    
045    }