Hadoop中求最高气温

我相信所有hadoop爱好者自己动手写的第一个程序都是求最高气温，下面大家可以参考一下

Hadoop中求最高气温

import java.io.IOException;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
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;


     class Map extends Mapper<LongWritable,Text,Text,IntWritable>{
    @Override
         public void map (LongWritable key, Text value, Context context)
            throws IOException,InterruptedException{
            String line = value.toString();
            String year = line.substring(15, 19);
            int airTemperature;
            if(line.charAt(25) == '+'){
                airTemperature = Integer.parseInt(line.substring(26, 30));
            }
            else{
                airTemperature = Integer.parseInt(line.substring(25, 30));
            }
            context.write(new Text(year), new IntWritable(airTemperature));
            
        }
    }
    class Reduce extends Reducer<Text,IntWritable,Text,IntWritable>{
    @Override
        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(new Text(key), new IntWritable(maxValue));
        }
    }
    public class TemperatureMax {
    public static void main(String[] args) throws Exception{
        if (args.length != 2){
            System.err.println("can shu shao yu liang ge");
            System.exit(-1);
        }
    
        Job job = new Job();
        job.setJarByClass( TemperatureMax.class);
        job.setJobName("MyFirst");
        
        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        job.setMapperClass(Map.class);
        job.setReducerClass(Reduce.class);

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