在hadoop中查找最大值

import java.io.IOException;
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 MaxValueFinder {
  
  public static class MaxValueMapper extends Mapper<Object, Text, Text, IntWritable>{
    
    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();
    
    public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
      String[] values = value.toString().split(",");
      for (String val : values) {
        word.set("max");
        context.write(word, new IntWritable(Integer.parseInt(val)));
      }
    }
  }
  
  public static class MaxValueReducer 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 max = Integer.MIN_VALUE;
      for (IntWritable val : values) {
        max = Math.max(max, val.get());
      }
      result.set(max);
      context.write(key, result);
    }
  }
  
  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(conf, "max value finder");
    job.setJarByClass(MaxValueFinder.class);
    job.setMapperClass(MaxValueMapper.class);
    job.setCombinerClass(MaxValueReducer.class);
    job.setReducerClass(MaxValueReducer.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);
  }
}