Write a Word Count Program in Hadoop using MapReduce?

 Here we have 3 classes one for Mapper, one for Reducer and one main class for word count.

Map.Java

package Hadoop.Practice;

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

import java.io.IOException;
import java.util.StringTokenizer;


import org.apache.hadoop.io.*;


public class Map extends Mapper<LongWritable, Text, Text, IntWritable>
{ 
   @Override
   public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException
   {
	   IntWritable one = new IntWritable(1);
	   Text word = new Text();
	   
	   String line = value.toString();
	   StringTokenizer tokens = new StringTokenizer(line);
	   
	   while(tokens.hasMoreTokens())
	   {
		   word.set(tokens.nextToken());
		   context.write(word, one);
	   }
   }
}

Reduce.Java

package Hadoop.Practice;

import java.io.IOException;
import java.util.Iterator;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;


public class Reduce extends Reducer<Text, IntWritable, Text, IntWritable>
{
	@Override
	public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException
	{
		int sum = 0;
		
		Iterator<IntWritable> itr = values.iterator(); 
		
		while(itr.hasNext())
		{
			sum += itr.next().get();
		}
		
		context.write(key, new IntWritable(sum));
	}
}

WordCount.java

package Hadoop.Practice;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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 WordCount 
{
	public static void main(String args[])
	{
		try
		{
			Job job = Job.getInstance();
			job.setJobName("Word Count Job");
			job.setJarByClass(WordCount.class);
			job.setOutputKeyClass(Text.class);
			job.setOutputValueClass(IntWritable.class);
			job.setMapperClass(Map.class);
			job.setReducerClass(Reduce.class);
			job.setInputFormatClass(TextInputFormat.class);
			job.setOutputFormatClass(TextOutputFormat.class);
			
			FileInputFormat.addInputPath(job, new Path(args[0]));
			FileOutputFormat.setOutputPath(job, new Path(args[1]));
			
			job.waitForCompletion(true);
		}
		catch(Exception e)
		{
			e.printStackTrace();
		}
	}
}