AvgScore.java

package he.cn;

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.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.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class AvgScore {
	public static class Map extends Mapper<LongWritable, Text, Text, IntWritable> {
		public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
			String[] split = value.toString().split("\t");
			String Sno = split[0];
			int Score = Integer.parseInt(split[2]);
			context.write(new Text(Sno), new IntWritable(Score));
		}
	}

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

	}

	public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
		Configuration conf = new Configuration();
		String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
		if (otherArgs.length != 2) {
			System.err.println("Usage: Score Average<int><out>");
			System.exit(2);
		}
		Job job = Job.getInstance(conf, "score");
		job.setJar("avgscore2.jar");
		job.setJarByClass(AvgScore.class);
		job.setMapperClass(Map.class);
		job.setReducerClass(Reduce.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		job.setInputFormatClass(TextInputFormat.class);
		job.setOutputFormatClass(TextOutputFormat.class);
		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
		System.exit(job.waitForCompletion(true) ? 0 : 1);
		System.out.println("Over!");
	}

}