com.binbo.wordcount.WordCount.java Source code

Introduction

Here is the source code for com.binbo.wordcount.WordCount.java

Source

/**
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package com.binbo.wordcount;

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Partitioner;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class WordCount {

    public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable> {

        private final static IntWritable one = new IntWritable(1);
        private Text mWord = new Text();

        public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
            StringTokenizer itr = new StringTokenizer(value.toString());
            while (itr.hasMoreTokens()) {
                mWord.set(itr.nextToken());
                // We only want to count real words starting with letters
                // "m", "n", "o", "p", and "q" (no matter if they are
                // capitalized or not)
                int c = mWord.charAt(0);
                if (c == 'm' || c == 'M' || c == 'n' || c == 'N' || c == 'o' || c == 'O' || c == 'p' || c == 'P'
                        || c == 'q' || c == 'Q') {
                    context.write(mWord, one);
                }
            }
        }
    }

    // The custom partitioner to this Word Count program
    public static class WordPartitioner extends Partitioner<Text, IntWritable> {

        @Override
        public int getPartition(Text key, IntWritable value, int numPartitions) {
            // this is done to avoid performing mod with 0
            if (numPartitions == 0) {
                return 0;
            }

            // Assign words starting with "M" or "m" to reduce task 0,
            // those starting with "N" or "n" to task 1, and so on.
            int target = 0;
            switch (key.charAt(0)) {
            case 'm':
            case 'M':
                target = 0;
                break;
            case 'n':
            case 'N':
                target = 1 % numPartitions;
                break;
            case 'o':
            case 'O':
                target = 2 % numPartitions;
                break;
            case 'p':
            case 'P':
                target = 3 % numPartitions;
                break;
            case 'q':
            case 'Q':
                target = 4 % numPartitions;
                break;
            }

            return target;
        }
    }

    public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
        private IntWritable result = new IntWritable();

        public void reduce(Text key, Iterable<IntWritable> values, Context context)
                throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable val : values) {
                sum += val.get();
            }
            result.set(sum);
            context.write(key, result);
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
        if (otherArgs.length != 2) {
            System.err.println("Usage: wordcount <in> <out>");
            System.exit(2);
        }
        Job job = new Job(conf, "word count");
        job.setJarByClass(WordCount.class);
        job.setMapperClass(TokenizerMapper.class);
        job.setCombinerClass(IntSumReducer.class); // Set the combiner
        job.setPartitionerClass(WordPartitioner.class);
        job.setReducerClass(IntSumReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
        FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}