结果：（不是很理解，为啥去掉iterable后就只输出一个value  key哪去了呢）

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.NullWritable;

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.input.TextInputFormat;

import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class MySort {

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

        private IntWritable val = new IntWritable();

        public void map(Object key, Text value, Context context) throws IOException, InterruptedException{

            String line = value.toString().trim();

            val.set(Integer.parseInt(line));

            context.write(val, NullWritable.get());

        }

    }

    public static class IntSortReducer extends Reducer<IntWritable, NullWritable, IntWritable,IntWritable>{

        private static IntWritable num = new IntWritable();

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

            for (NullWritable value : values) {

                context.write(num, key);

                num = new IntWritable(num.get() + );

            }

        }

    }

    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {

        String dir_in = "hdfs://localhost:9000/in_sort";

        String dir_out = "hdfs://localhost:9000/out_sort";

        Path in = new Path(dir_in);

        Path out = new Path(dir_out);

        Configuration conf = new Configuration();

        Job sortJob = new Job(conf, "my_sort");

        sortJob.setJarByClass(MySort.class);

        sortJob.setInputFormatClass(TextInputFormat.class);

        sortJob.setMapperClass(IntSortMapper.class);

        //sortJob.setCombinerClass(SortReducer.class);

        //countJob.setPartitionerClass(HashPartitioner.class);

        sortJob.setMapOutputKeyClass(IntWritable.class);

        sortJob.setMapOutputValueClass(NullWritable.class);

        FileInputFormat.addInputPath(sortJob, in);

        sortJob.setReducerClass(IntSortReducer.class);

        sortJob.setNumReduceTasks();

        sortJob.setOutputKeyClass(IntWritable.class);

        sortJob.setOutputValueClass(IntWritable.class);

        //countJob.setOutputFormatClass(SequenceFileOutputFormat.class);

        FileOutputFormat.setOutputPath(sortJob, out);

        sortJob.waitForCompletion(true);

    }

}
1    2
2    6
3    15
4    22
5    26
6    32
7    32
8    54
9    92
10    650
11    654
12    756
13    5956
14    65223