头文件：

//package com.company;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableComparable;
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.input.SequenceFileInputFormat;
import org.apache.hadoop.mapreduce.lib.map.InverseMapper;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

import java.io.*;
import java.util.Random;
import java.util.StringTokenizer;

剩余代码部分

public class WordCount {
 
    public static class TokenizerMapper
            extends Mapper<Object, Text, Text, IntWritable>{
        private final static IntWritable one = new IntWritable(1);
        private 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());
                context.write(word, one);
            }
        }
    }
    public static class TokenizerMapper2
            extends Mapper<Object, Text,IntWritable,Text>{
        int c=0;
        public void map(Object key, Text value, Context context
        ) throws IOException, InterruptedException {
            StringTokenizer itr = new StringTokenizer(value.toString());
            IntWritable a=new IntWritable(Integer.parseInt(itr.nextToken()));
            Text b=new Text(itr.nextToken());
            if((c<100)&b.getLength()>5){
                context.write(a, b);
                c++;
            }
        }
    }
    private static class IntWritableDecreasingComparator extends IntWritable.Comparator {
        public int compare(WritableComparable a, WritableComparable b) {
            //System.out.println("ss");
            return -super.compare(a, b);
        }

        public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) {
            //System.out.println("ss1");
            return -super.compare(b1, s1, l1, b2, s2, l2);
        }
    }
    public static class IntSumReducer
            extends Reducer<Text,IntWritable,Text,IntWritable> {

        private IntWritable result = new IntWritable();
        int number=0;

        public void reduce(Text key, Iterable<IntWritable> values,
                           Context context
        ) throws IOException, InterruptedException {
             int sum = 0;
             for (IntWritable val : values) {
                 sum += val.get();
             }
                 result.set(sum);
             context.write(key, result);
         }
    }
    public static void Write(String name){
        try
        {
            Configuration conf=new Configuration();
            conf.set("fs.defaultFS", "hdfs://localhost:9000");
            conf.set("fs.hdfs.omp", "org.apache.hadoop.hdfs.DistributedFileSystem");
            FileSystem fs=FileSystem.get(conf);
            FSDataOutputStream os=fs.create(new Path(name));
            BufferedReader br=new BufferedReader(new FileReader("output//part-r-00000"));
            String str=null;
            int n=1;
            while((str=br.readLine())!=null){
                str=str+"\n";
                byte[] buff=str.getBytes();
                os.write(buff,0,buff.length);
                if(n<=10){
                    System.out.println(str);
                }n++;
            }
            br.close();
            os.close();
            fs.close();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        String[] otherArgs = new GenericOptionsParser(conf, args)
                .getRemainingArgs();
        if (otherArgs.length != 2) {
            System.err.println("Usage: wordcount <in> <out>");
            System.exit(2);
        }
        Path tempDir = new Path("wordcount-temp1-" + Integer.toString(
                new Random().nextInt(Integer.MAX_VALUE))); //定义一个临时目录
        Job job = new Job(conf, "word count");
        job.setJarByClass(WordCount.class);
        try{
            job.setMapperClass(TokenizerMapper.class);
            job.setCombinerClass(IntSumReducer.class);
            job.setReducerClass(IntSumReducer.class);
            job.setOutputKeyClass(Text.class);
            job.setOutputValueClass(IntWritable.class);
            FileInputFormat.addInputPath(job, new Path("hdfs://localhost:9000/input/book.txt"));
            FileOutputFormat.setOutputPath(job, tempDir);//先将词频统计任务的输出结果写到临时目
            //录中, 下一个排序任务以临时目录为输入目录。
            job.setOutputFormatClass(SequenceFileOutputFormat.class);
            if(job.waitForCompletion(true))
            {
                Job sortJob = new Job(conf, "sort");
                sortJob.setJarByClass(WordCount.class);
                FileInputFormat.addInputPath(sortJob, tempDir);
                sortJob.setInputFormatClass(SequenceFileInputFormat.class);
                /*InverseMapper由hadoop库提供，作用是实现map()之后的数据对的key和value交换*/
                sortJob.setMapperClass(InverseMapper.class);
                /*将 Reducer 的个数限定为1, 最终输出的结果文件就是一个。*/
                sortJob.setNumReduceTasks(1);
                FileOutputFormat.setOutputPath(sortJob,new Path("hdfs://localhost:9000/output"));
                sortJob.setOutputKeyClass(IntWritable.class);
                sortJob.setOutputValueClass(Text.class);//升序排序ok
                sortJob.setSortComparatorClass(IntWritableDecreasingComparator.class);
                if(sortJob.waitForCompletion(true)){
                    Write("result");
                }else{
                    System.out.println("1-- not");
                    System.exit(1);
                }
                System.exit(sortJob.waitForCompletion(true) ? 0 : 1);
            }
        }finally{
            FileSystem.get(conf).deleteOnExit(tempDir);
        }
    }
}