1.txt

dong xi cheng

xi dong cheng

wo ai beijing

tian an men

qiche

dong

dong

dong

2.txt

dong xi cheng

xi dong cheng

wo ai beijing

tian an men

qiche

dong

dong

dong

import java.io.IOException;

import java.util.Random;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.FileSystem;

import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.LongWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Job;

import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;

import org.apache.hadoop.mapreduce.lib.input.SequenceFileInputFormat;

import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;

import org.apache.hadoop.mapreduce.lib.map.InverseMapper;

import org.apache.hadoop.mapreduce.lib.map.RegexMapper;

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

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

import org.apache.hadoop.mapreduce.lib.partition.HashPartitioner;

import org.apache.hadoop.mapreduce.lib.reduce.LongSumReducer;

public class IGrep {

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

            ClassNotFoundException, InterruptedException {

        Configuration conf = new Configuration();

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

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

        String reg = ".ng";//匹配三个字符的字符串，且以ng结尾。

        conf.set(RegexMapper.PATTERN, reg);

        conf.setInt(RegexMapper.GROUP, 0);

        Path in = new Path(dir_in);

        Path tmp = new Path("grep-temp-"

                + Integer.toString(new Random().nextInt(Integer.MAX_VALUE)));

        Path out = new Path(dir_out);

        try {

            Job grepJob = new Job(conf, "grep-search");

            grepJob.setJarByClass(IGrep.class);

            grepJob.setInputFormatClass(TextInputFormat.class);

            grepJob.setMapperClass(RegexMapper.class);

            grepJob.setCombinerClass(LongSumReducer.class);

            grepJob.setPartitionerClass(HashPartitioner.class);

            grepJob.setMapOutputKeyClass(Text.class);

            grepJob.setMapOutputValueClass(LongWritable.class);

            FileInputFormat.addInputPath(grepJob, in);

            grepJob.setReducerClass(LongSumReducer.class);

            // job.setNumReduceTasks(1);

            grepJob.setOutputFormatClass(SequenceFileOutputFormat.class);

            grepJob.setOutputKeyClass(Text.class);

            grepJob.setOutputValueClass(LongWritable.class);

            FileOutputFormat.setOutputPath(grepJob, tmp);

            grepJob.waitForCompletion(true);

            Job sortJob = new Job(conf, "grep-sort");

            sortJob.setJarByClass(IGrep.class);

            sortJob.setInputFormatClass(SequenceFileInputFormat.class);

            sortJob.setMapperClass(InverseMapper.class);

            FileInputFormat.addInputPath(sortJob, tmp);

            sortJob.setNumReduceTasks(1);【全局排序】

            sortJob.setSortComparatorClass(LongWritable.DecreasingComparator.class);//逆序

            FileOutputFormat.setOutputPath(sortJob, out);

            sortJob.waitForCompletion(true);

        } finally {

            FileSystem.get(conf).delete(tmp, true);

        }

    }

}

输出结果：
10    ong
4    eng
2    ing