reduce side join

import java.io.IOException;

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;

public class ReduceJoin {

	public static class CustsMapper extends
			Mapper<Object, Text, Text, Text> {
		public void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {
//  4000001,Kristina,Chung,55,Pilot
			String record = value.toString();
			String[] parts = record.split(",");
			context.write(new Text(parts[0]), new Text("custs\t" + parts[1])); // key is th id, the common fields between the 2 files in input
		}
	}

	public static class TxnsMapper extends
			Mapper<Object, Text, Text, Text> {
		public void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {
//00000000,06-26-2011,4000001,040.33,Exercise & Fitness,Cardio Machine Accessories,Clarksville,Tennessee,credit
			String record = value.toString();
			String[] parts = record.split(",");
			context.write(new Text(parts[2]), new Text("txns\t" + parts[3])); // emit id and what we wnt to join
		}
	}

	public static class ReduceJoinReducer extends
			Reducer<Text, Text, Text, Text> {
		public void reduce(Text key, Iterable<Text> values, Context context)
				throws IOException, InterruptedException {
// the reducer works on (key, L(Values)) so in the values we have custs and txns
			String name = "";
			double total = 0.0;
			int count = 0;
			for (Text t : values) { // in values we have 1 value for the custmoer info and all the related txns related infor to the customer, because we have cust id as key for both
				String parts[] = t.toString().split("\t");
				if (parts[0].equals("txns")) { // logic to undertand what is the value about
					count++;
					total += Float.parseFloat(parts[1]);
				} else if (parts[0].equals("custs")) {
					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);
		
	// define the multile inputs and the 2 mappers
		MultipleInputs.addInputPath(job, new Path(args[0]),TextInputFormat.class, CustsMapper.class);
		MultipleInputs.addInputPath(job, new Path(args[1]),TextInputFormat.class, TxnsMapper.class);
		Path outputPath = new Path(args[2]);
		
		
		FileOutputFormat.setOutputPath(job, outputPath);
		outputPath.getFileSystem(conf).delete(outputPath);
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}