How to run WordCount.java Program on hadoop - Conventional Method

# Program on WordCount.java

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

import org.apache.hadoop.conf.Configuration;
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.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class WordCount
{
  public static class TokenizerMapper
       extends Mapper<Object, Text, Text, IntWritable>
   {

    private Text word = new Text();
    private final static IntWritable one = new IntWritable(1);
    public void map(Object key, Text value, Context context)
                      throws IOException, InterruptedException
    {
      StringTokenizer itr = new StringTokenizer(value.toString());
      while (itr.hasMoreTokens())
      {
        word.set(itr.nextToken());
        context.write(word, one);
      }
    }
  }

  public static class IntSumReducer
    extends Reducer<Text,IntWritable,Text,IntWritable>
  {
    private IntWritable result = new IntWritable();
    public void reduce(Text key, Iterable<IntWritable> values, Context context)
                  throws IOException, InterruptedException
    {
      int sum = 0;
      for (IntWritable val : values)
      {
        sum += val.get();
      }
      result.set(sum);
      context.write(key, result);
    }
  }

  public static void main(String[] args)
     throws Exception
   {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(conf, "word count");
    job.setJarByClass(WordCount.class);
    job.setMapperClass(TokenizerMapper.class);
    job.setCombinerClass(IntSumReducer.class);
    job.setReducerClass(IntSumReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}
 

How to run WordCount.java Program on hadoop  

Step 1:  create a directory rkmapreduce on the local file system and then place the  file WordCount.java  in it as shown

Step 2: create a class files to the WordCount.java file using the following command

javac -classpath `hadoop classpath` -d /home/hduser/rkmapreduce/ WordCount.java

Step 3: create a jar file wc.jar in the directory rkmapreduce as shown 

jar -cvf wc.jar -C /home/hduser/rkmapreduce/ .

Step 4: create an input file input.txt that we need to check the wordcount of it as shown

Step 5: Now place the created input file input.txt into hadoop cluster by creating a directory rkmr in it as shown

hdfs dfs -mkdir  /rkmr 

hdfs dfs -put /home/hduser/rkmapreduce/input.txt  /rkmr

Now we can check the content of the file rkmr/input.txt using the command

hdfs dfs -cat /rkmr/input.txt

Step 6: Now run the command hadoop jar to WordCount the file as shown 

 hadoop jar wc.jar WordCount /rkmr/input.txt /rkmr/output

Step 7: Now we can check the output of wordcount program using the following command

hdfs dfs -lsr /rkmr

hdfs dfs -cat /rkmr/output/part*

Step 8: using fsck command you can check the details of the stored file in hdfs/hadoop

hdfs fsck /rkmr/input.txt