ReduceJoin.java

package org.hadoop;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
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.MultipleInputs;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import java.io.IOException;

/**
 * @author Krisztian_Horvath
 */
public class ReduceJoin {

    public static class SalesRecordMapper extends Mapper<Object, Text, Text, Text> {
        public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
            String record = value.toString();
            String[] parts = record.split("\t");
            context.write(new Text(parts[0]), new Text("sales\t" + parts[1]));
        }
    }

    public static class AccountRecordMapper extends Mapper<Object, Text, Text, Text> {
        public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
            String record = value.toString();
            String[] parts = record.split("\t");
            context.write(new Text(parts[0]), new Text("accounts\t" + parts[1]));
        }
    }

    public static class ReduceJoinReducer extends Reducer<Text, Text, Text, Text> {
        public void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
            String name = "";
            double total = 0.0;
            int count = 0;
            for (Text t : values) {
                String parts[] = t.toString().split("\t");
                if (parts[0].equals("sales")) {
                    count++;
                    total += Float.parseFloat(parts[1]);
                } else if (parts[0].equals("accounts")) {
                    name = parts[1];
                }
            }
            String str = String.format("%d\t%f", count, total);
            context.write(new Text(name), new Text(str));
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = new Job(conf, "Reduce-side join");
        job.setJarByClass(ReduceJoin.class);
        job.setReducerClass(ReduceJoinReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        MultipleInputs.addInputPath(job, new Path(args[0]), TextInputFormat.class, SalesRecordMapper.class);
        MultipleInputs.addInputPath(job, new Path(args[1]), TextInputFormat.class, AccountRecordMapper.class);
        Path outputPath = new Path(args[2]);
        FileOutputFormat.setOutputPath(job, outputPath);
        outputPath.getFileSystem(conf).delete(outputPath, true);
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}