hadoopが持参したWordCountプログラム

hadoopは擬似分布モードで動作する.
1つの文章に単語が現れる回数を統計します.
コードは次のとおりです.

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.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class CiHui {

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

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

		public void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {
			String line = value.toString();
			StringTokenizer itr = new StringTokenizer(line);
			while (itr.hasMoreTokens()) {
				word.set(itr.nextToken());
				context.write(new Text(word), one);
			}

		}
	}

	public static class CiHuiReducer extends
			Reducer<Text, IntWritable, Text, IntWritable> {
		private IntWritable res = 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();
			}
			res.set(sum);
			context.write(key, res);

		}
	}

	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		if (args.length != 2) {
			System.err.println("Usage: cihui <in> <out>");
			System.exit(2);
		}
		Job job = new Job(conf, "ci hui");
		job.setJarByClass(CiHui.class);
		job.setMapperClass(CiHuiMapper.class);
		job.setCombinerClass(CiHuiReducer.class);
		job.setReducerClass(CiHuiReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		FileInputFormat.addInputPath(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}

eclipseで実行し、パラメータは次のように入力します.
hdfs://localhost:9000/user/tom/input   hdfs://localhost:9000/user/tom/output
実行結果は次のとおりです.
a    4 and    5 hadoop    7 hello    5 java    6 txt    6