CountSort.java

import java.io.IOException;
import java.util.*;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.util.*;

public class CountSort{

  public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, IntWritable, Text> {
    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();

    public void map(LongWritable key, Text value, OutputCollector<IntWritable,Text> output, Reporter reporter) throws IOException {
      String line = value.toString();
      StringTokenizer tokenizer = new StringTokenizer(line);
      while (tokenizer.hasMoreTokens()) {
        word.set(tokenizer.nextToken());
        output.collect(new IntWritable(Integer.valueOf(tokenizer.nextToken())),word);
      }
    }
  }

  public static class Reduce extends MapReduceBase implements Reducer<IntWritable, Text, IntWritable, Text> {
    public void reduce(IntWritable key, Iterator<Text> values, OutputCollector<IntWritable, Text> output, Reporter reporter) throws IOException {
      while (values.hasNext()) {
        output.collect(key, new Text(values.next()));
      } 
    }
  }

  public static void main(String[] args) throws Exception {
    JobConf conf = new JobConf(CountSort.class);
    conf.setJobName("countsort");

    conf.setOutputKeyClass(IntWritable.class);
    conf.setOutputValueClass(Text.class);

    conf.setMapperClass(Map.class);
    conf.setCombinerClass(Reduce.class);
    conf.setReducerClass(Reduce.class);

    conf.setInputFormat(TextInputFormat.class);
    conf.setOutputFormat(TextOutputFormat.class);

    FileInputFormat.setInputPaths(conf, new Path(args[0]));
    FileOutputFormat.setOutputPath(conf, new Path(args[1]));

    JobClient.runJob(conf);
  }
}