MapReduce自帶wordcount的實現

package com.bruce.mapreduce;

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.LongWritable;
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 WordCount {

	// step 1: Map Class
	/**
	 * Mapper<KEYIN, VALUEIN, KEYOUT, VALUEOUT>
	 * 
	 */
	public static class WordCountMapper extends
			Mapper<LongWritable, Text, Text, IntWritable> {
		private Text mapOutputKey = new Text();
		private final static IntWritable mapOutputValue = new IntWritable(1);

		@Override
		protected void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {
			// TODO Auto-generated method stub
			//line value
			String lineValue = value.toString();
			//split
			StringTokenizer stringTokenizer = new StringTokenizer(lineValue);
			
			//iterator
			while(stringTokenizer.hasMoreElements()){
				//get value
				String wordValue = stringTokenizer.nextToken();
				//set value
				mapOutputKey.set(wordValue);
				//output
				context.write(mapOutputKey, mapOutputValue);
			}
		}

	}

	// step 2: Reduce Class
	/**
	 * Reducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT>
	 * 
	 */
	public static class WordCountReducer extends
			Reducer<Text, IntWritable, Text, IntWritable> {
		private IntWritable outputValue = new IntWritable();

		@Override
		protected void reduce(Text key, Iterable<IntWritable> values,
				Context context) throws IOException, InterruptedException {
			// TODO Auto-generated method stub
			//sum tmp
			int sum = 0;
			//iterator
			for(IntWritable value: values){
				//total
				sum += value.get();
			}
			//set value
			outputValue.set(sum);
			//output
			context.write(key, outputValue);
		}

	}

	// step 3: Driver ,component job
	public int run(String[] args) throws Exception {
		// 1: get configration
		Configuration configuration = new Configuration();
		
		// 2: create Job
		Job job = Job.getInstance(configuration, this.getClass()
				.getSimpleName());
		// run jar
		job.setJarByClass(this.getClass());
		
		// 3: set job
		// input -> map -> reduce -> output
		// 3.1 input
		Path inPath = new Path(args[0]);
		FileInputFormat.addInputPath(job, inPath);

		// 3.2: map
		job.setMapperClass(WordCountMapper.class);
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(IntWritable.class);

		// 3.3: reduce
		job.setReducerClass(WordCountReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);

		// 3.4: output
		Path outPath = new Path(args[1]);
		FileOutputFormat.setOutputPath(job, outPath);

		// 4: submit job
		boolean isSuccess = job.waitForCompletion(true);

		return isSuccess ? 0 : 1;
	}

	//step 4: run program
	public static void main(String[] args) throws Exception {
		int status = new WordCount().run(args);
		System.exit(status);

	}
}