问题代码（wordcount）

package com.hadoop.mrdemo;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
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.util.StringUtils;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

public class WordCountJob extends Configured implements Tool {

public static class WordCountMapper extends Mapper<LongWritable, Text, Text, LongWritable> {

    private Text word = new Text();
    private LongWritable one = new LongWritable(1);
    @Override
    protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, LongWritable>.Context context)
            throws IOException, InterruptedException {
        String[] words = StringUtils.split(value.toString(),' ');
        for(String w : words){
            word.set(w);
            context.write(word, one);
        }
    }

}

public static class WordCountReducer extends Reducer<Text,LongWritable,Text,LongWritable>{

    private LongWritable result = new LongWritable();

    @Override
    protected void reduce(Text key, Iterable<LongWritable> values,
            Reducer<Text, LongWritable, Text, LongWritable>.Context context) throws IOException, InterruptedException {
        long sum = 0L;
        for(LongWritable v : values){
            sum +=v.get();
        }
        result.set(sum);
        context.write(key, result);
    }

}

@Override
public int run(String[] args) throws Exception  {
    // TODO Auto-generated method stub
    if(args.length <2){
        System.out.println("<input dir> <output dir>");
        return 2;
    }
    Job job =Job.getInstance(getConf(), "WordCountJob");
    job.setJarByClass(WordCountJob.class);
    job.setMapperClass(WordCountMapper.class);
    job.setReducerClass(WordCountReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(LongWritable.class);

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

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

public static void main(String[] args) throws Exception  {
    // TODO Auto-generated method stub
    int res = ToolRunner.run(new WordCountJob(), args);
    System.exit(res);
}

}