Code example by Apache Spark

This class will read the text file in the HDFS and counts the number of occurrences of each word in a given paragraph. The result will be exported to a new file in HDFS.

import java.io.IOException;
import java.util.*;

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 WordCount1 {
    public static class WordCountMap extends Mapper<Object, Text, Text, IntWritable> {
        @Override
        public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
	    String line = value.toString();    // each value is one line in the paragraph
	    StringTokenizer tokenizer = new StringTokenizer(line);
            while (tokenizer.hasMoreTokens()) {
	        String nextToken = tokenizer.nextToken();
		context.write(new Text(nextToken), new IntWritable(1));
	    }
	}
    }

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

    public static void main(String[] args) throws Exception {
        Job job = Job.getInstance(new Configuration(), "wordcount");
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        job.setMapperClass(WordCountMap.class);
        job.setReducerClass(WordCountReduce.class);

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

        job.setJarByClass(WordCount1.class);
	System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}