wordcount的mr java代码

package 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.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> {
		// define the constant number ONE
		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 {
			StringTokenizer itr = new StringTokenizer(value.toString());
			while (itr.hasMoreTokens()) {
				word.set(itr.nextToken());
				context.write(word, one);
			}
		}
	}

	/**
	 * the reducer class calculate the count sum of each word
	 * INPUT: KEY: text VALUE: IntWritable
	 * OUTPUT:KEY:text VALUE: IntWritable
	 */
	public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
		private IntWritable result = new IntWritable();
		// values are the set of each node or file
		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);
		}
	}

	/**
	 * 
	 * @param args
	 * @throws Exception
	 *             one arguments is the input path the other arguments is the
	 *             output path
	 */
	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 = Job.getInstance(conf, "Word count");
		job.setJarByClass(WordCount.class);
		job.setJobName("Word count test");

		job.setMapperClass(TokenizerMapper.class);

		// combiner use the same method as reducer and calculate the local count
		// sum
		job.setCombinerClass(IntSumReducer.class);

		// reducer task get the total count of each word
		job.setReducerClass(IntSumReducer.class);

		// set the output KEY and VALUE type
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);

		// use the arguments to set the job input and output path
		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));

		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}