MapReduce编程：数字排序

问题描述

将乱序数字按照升序排序。

 

思路描述

按照mapreduce的默认排序，依次输出key值。

 

代码

package org.apache.hadoop.examples;

import java.io.IOException;
import java.util.Iterator;
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 sort {
    public sort() {
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();

        String fileAddress = "hdfs://localhost:9000/user/hadoop/";

        //String[] otherArgs = (new GenericOptionsParser(conf, args)).getRemainingArgs();
        String[] otherArgs = new String[]{fileAddress+"number.txt", fileAddress+"output"};
        if(otherArgs.length < 2) {
            System.err.println("Usage: sort <in> [<in>...] <out>");
            System.exit(2);
        }

        Job job = Job.getInstance(conf, "sort");
        job.setJarByClass(sort.class);
        job.setMapperClass(sort.TokenizerMapper.class);
        //job.setCombinerClass(sort.SortReducer.class);
        job.setReducerClass(sort.SortReducer.class);
        job.setOutputKeyClass(IntWritable.class);
        job.setOutputValueClass(IntWritable.class);

        for(int i = 0; i < otherArgs.length - 1; ++i) {
            FileInputFormat.addInputPath(job, new Path(otherArgs[i]));
        }

        FileOutputFormat.setOutputPath(job, new Path(otherArgs[otherArgs.length - 1]));
        System.exit(job.waitForCompletion(true)?0:1);
    }


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

        public TokenizerMapper() {
        }

        public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
            StringTokenizer itr = new StringTokenizer(value.toString());

            while(itr.hasMoreTokens()) {
                context.write(new IntWritable(Integer.parseInt(itr.nextToken())), new IntWritable(1));
            }

        }
    }


    public static class SortReducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {

        private static IntWritable num = new IntWritable(1);

        public SortReducer() {
        }

        public void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {

            for(Iterator<IntWritable> i$ = values.iterator(); i$.hasNext();i$.next()) {
                context.write(num, key);
            }
           num = new IntWritable(num.get()+1);
        }
    }

}

 

注：不能有combiner操作。

不然就会变成