Code shows how to implement a mapper only Hadoop Job

Map.java

package org.dedunumax.mapperOnly;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class Map extends Mapper<LongWritable, Text, Text, Text> {

	public void map(LongWritable key, Text value, Context context)
			throws IOException, InterruptedException {
		// Do what ever you want here
		context.write(value,null);
	}

}

MapOnly.java

package org.dedunumax.mapperOnly;

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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

public class App 
{
    public static void main( String[] args ) throws IOException, ClassNotFoundException, InterruptedException
    {
    	Configuration conf = new Configuration();
	Job job = new Job(conf, "Mapper_Only_Job");

	job.setJarByClass(App.class);
	job.setMapperClass(Map.class);
	job.setOutputKeyClass(Text.class);
	job.setOutputValueClass(Text.class);
	job.setInputFormatClass(TextInputFormat.class);
	job.setOutputFormatClass(TextOutputFormat.class);
		
	// Sets reducer tasks to 0
	job.setNumReduceTasks(0);

	FileInputFormat.addInputPath(job, new Path(args[0]));
	FileOutputFormat.setOutputPath(job, new Path(args[1]));

	boolean result = job.waitForCompletion(true);

	System.exit(result ? 0 : 1);
    }
}