Hadoop计算平均值【转】

package org.apache.hadoop.examples;

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.DoubleWritable;
//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 Average {

    public static class AverageMaper extends Mapper<Object,Text,Text,Text>
    {
        //private final static IntWritable one=new IntWritable(1);
        private static 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());
                if(itr.hasMoreTokens())
                    context.write(word, new Text(itr.nextToken()+",1"));
            }
        }
    }
    public static class AveragerCombine extends Reducer<Text,Text,Text,Text>
    {
        public void reduce(Text key,Iterable<Text> values,Context context) throws
        IOException,InterruptedException
        {
            int sum=0;
            int cnt=0;
            for(Text val:values)
            {
                String []str=val.toString().split(",");
                sum+=Integer.parseInt(str[0]);
                cnt+=Integer.parseInt(str[1]);
            }
            context.write(key,new Text(sum+","+cnt));
        }
    }
    public static class AveragerReduce extends Reducer<Text,Text,Text,DoubleWritable>
    {
        public void reduce(Text key,Iterable<Text> values,Context context) throws 
        IOException,InterruptedException
        {
            int sum=0;
            int cnt=0;
            for(Text val:values)
            {
                String []str=val.toString().split(",");
                sum+=Integer.parseInt(str[0]);
                cnt+=Integer.parseInt(str[1]);                
            }
            double res=(sum*1.0)/cnt;
            context.write(key, new DoubleWritable(res));
        }
    }
    
    public static void main(String[] args) throws Exception{
        // TODO Auto-generated method stub
        Configuration conf=new Configuration();
        String []myargs=args;
        if(myargs.length!=2)
        {
            System.err.println("please input two args<in> <out>\n");
            System.exit(2);
        }
        Job job=new Job(conf,"average job");
        job.setJarByClass(Average.class);
        job.setMapperClass(AverageMaper.class);
        job.setCombinerClass(AveragerCombine.class);
        job.setReducerClass(AveragerReduce.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        FileInputFormat.addInputPath(job, new Path(myargs[0]));
        FileOutputFormat.setOutputPath(job,new Path(myargs[1]));
        System.exit(job.waitForCompletion(true)?0:1);
    }
}