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