Java MapReduce Program with example

This presentation will give an idea on how to write Java map reduce program.

//MaxTemperatureMapper Program
import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

class MaxTemperatureMapper
extends Mapper<LongWritable, Text, Text, IntWritable> {

 public void map(LongWritable key, Text value, Context context) throws IOException,InterruptedException {

  String line = value.toString();

  String year = line.substring(15, 19);
  int airTemperature = Integer.parseInt(line.substring(88, 92));

  context.write(new Text(year), new IntWritable(airTemperature));
 }
}

//MaxTemperatureReducer Program
import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

Class MaxTemperatureReducer
extends Reducer<Text, IntWritable, Text, IntWritable> {

 public void reduce(Text key, Iterable<IntWritable> values,
   Context context)throws IOException, InterruptedException {

  int maxValue = Integer.MIN_VALUE;

  for (IntWritable value : values) {
   maxValue = Math.max(maxValue, value.get());
  }

  context.write(key, new IntWritable(maxValue));
 }

//MaxTemperature  Program

 import java.io.IOException;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.io.IntWritable;
 import org.apache.hadoop.io.Text;
 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
 import org.apache.hadoop.mapreduce.Job;

 public class MaxTemperature {
  public static void main(String[] args) throws Exception {
   if (args.length != 2) {
    System.err.println("Usage: MaxTemperature <input path> <output path>");
    System.exit(-1);
   }

   Configuration conf = new Configuration();
   Job job = new Job(conf,â&#128;Max Tempâ&#128;);
   job.setJarByClass(MaxTemperature.class);

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

   job.setMapperClass(MaxTemperatureMapper.class);
   job.setReducerClass(MaxTemperatureReducer.class);

   job.setOutputKeyClass(Text.class);
   job.setOutputValueClass(IntWritable.class);

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