Hadoop学习笔记： MapReduce二次排序

本文给出一个实现MapReduce二次排序的例子

package SortTest;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.*;

public class SortComparable implements WritableComparable<SortComparable> {

    private Integer first;
    private Integer second;

    public SortComparable(){

    }

    public SortComparable(Integer first, Integer second) {
        this.first = first;
        this.second = second;
    }

    public Integer getFirst() {
        return first;
    }

    public Integer getSecond() {
        return second;
    }

    @Override
    public void readFields(DataInput in) throws IOException {
        this.first = in.readInt();
        this.second = in.readInt();
    }

    @Override
    public void write(DataOutput out) throws IOException {
        out.writeInt(this.first);
        out.writeInt(this.second);
    }

    @Override
    public int compareTo(SortComparable o) {
        int temp = this.first - o.first;
        if(temp != 0){
            return temp;
        } else {
            return (o.second - this.second);
        }
    }
}

package SortTest;

import java.io.IOException;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.*;
import org.apache.hadoop.mapreduce.lib.output.*;
import org.apache.hadoop.util.*;

public class SortComparableTest extends Configured implements Tool {

    public static class MapperTest extends Mapper<LongWritable, Text, SortComparable, IntWritable> {
        public void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            String[] split = value.toString().split("\t");
            Integer first = Integer.parseInt(split[0]);
            Integer second = Integer.parseInt(split[1]);
            SortComparable sc = new SortComparable(first, second);
            context.write(sc, new IntWritable(1));
        }
    }

    public static class ReducerTest extends Reducer<SortComparable, IntWritable, IntWritable, IntWritable> {
        public void reduce(SortComparable key, Iterable<IntWritable> values, Context context)
                throws IOException, InterruptedException {
            context.write(new IntWritable(key.getFirst()),new IntWritable(key.getSecond()));
        }
    }

    public static void main(String[] args) {
        try {
            int returnCode = ToolRunner.run(new SortComparableTest(), args);
            System.exit(returnCode);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    static final String INPUT = "/home/sortInput";
    static final String OUTPUT = "/home/sortOutput";

    @Override
    public int run(String[] arg0) throws Exception {
        Configuration conf = new Configuration();
        conf.set("fs.default.name","hdfs://localhost:9001");
        Job job = Job.getInstance(conf, "SortTest");

        FileInputFormat.addInputPath(job, new Path(INPUT));
        FileOutputFormat.setOutputPath(job, new Path(OUTPUT));

        job.setJarByClass(SortComparableTest.class);
        job.setMapperClass(MapperTest.class);
        job.setReducerClass(ReducerTest.class);

        job.setMapOutputKeyClass(SortComparable.class);
        job.setMapOutputValueClass(IntWritable.class);
        job.setOutputKeyClass(IntWritable.class);
        job.setOutputValueClass(IntWritable.class);

        job.waitForCompletion(true);
        return job.isSuccessful() ? 0 : 1;
    }

}