hw1.WordCount.java Source code

Introduction

Here is the source code for hw1.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 hw1;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
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.Reducer;
import org.apache.hadoop.mapreduce.Partitioner;
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 word = new Text();
        private HashMap<Text, IntWritable> h;

        protected void setup(Context context) throws IOException, InterruptedException {
            h = new HashMap<Text, IntWritable>();
        }

        public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
            StringTokenizer itr = new StringTokenizer(value.toString());
            while (itr.hasMoreTokens()) {
                word.set(itr.nextToken());
                // Get the first letter of the word
                int c = word.charAt(0);
                /*
                 * Make sure the real words starts with letters 'm','n','o','p'
                 * and 'q' (no matter if they are capitalized or not)
                 */
                if ((c >= 'M' && c <= 'Q') || (c >= 'm' && c <= 'q')) {
                    Text w = new Text(word);
                    if (h.containsKey(w)) {
                        IntWritable count = h.get(w);
                        count.set(count.get() + 1);
                        h.put(w, count);
                    } else {
                        h.put(w, new IntWritable(1));
                    }
                }
            }
        }

        protected void cleanup(Context context) throws IOException, InterruptedException {
            for (Map.Entry<Text, IntWritable> entry : h.entrySet()) {
                context.write(entry.getKey(), entry.getValue());
            }
        }
    }

    public static class CustomPartitioner extends Partitioner<Text, IntWritable> {
        @Override
        public int getPartition(Text key, IntWritable value, int numPartitions) {
            // Get the first letter of the key
            int c = key.charAt(0);
            // The index of the task it should assign to
            int index = 0;
            if (c == 'm' || c == 'M') {
                index = 0 % numPartitions;
            }
            if (c == 'n' || c == 'N') {
                index = 1 % numPartitions;
            }
            if (c == 'o' || c == 'O') {
                index = 2 % numPartitions;
            }
            if (c == 'p' || c == 'P') {
                index = 3 % numPartitions;
            }
            if (c == 'q' || c == 'Q') {
                index = 4 % numPartitions;
            }
            return index;
        }
    }

    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");
        /*
         * The line below can set the amount of reduce tasks to a specific
         * number, which equals to the amount of output 'part-r-...' files
         */
        // job.setNumReduceTasks(5);
        job.setJarByClass(WordCount.class);
        job.setMapperClass(TokenizerMapper.class);
        // job.setCombinerClass(IntSumReducer.class);
        job.setPartitionerClass(CustomPartitioner.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);
    }
}