code.java

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

public class MaxTemperature {

    public static class TempMapper extends Mapper<LongWritable, Text, Text, IntWritable> {

        private final static int MISSING = 9999;

        public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String line = value.toString();
            String[] fields = line.split(",");
            String year = fields[0].trim();
            String station = fields[1].trim();
            String tempStr = fields[2].trim();
            if (!tempStr.equals("Max Temperature")) {
                int temperature = Integer.parseInt(tempStr.substring(0, tempStr.indexOf("°F")).trim());
                context.write(new Text(year), new IntWritable(temperature));
            }
        }
    }

    public static class TempReducer extends Reducer<Text, IntWritable, Text, IntWritable> {

        public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            int maxTemp = Integer.MIN_VALUE;
            for (IntWritable value : values) {
                int temp = value.get();
                if (temp > maxTemp) {
                    maxTemp = temp;
                }
            }
            context.write(key, new IntWritable(maxTemp));
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "max temperature");
        job.setJarByClass(MaxTemperature.class);
        job.setMapperClass(TempMapper.class);
        job.setReducerClass(TempReducer.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);
    }
}