mao/reduce实现求平均值

 import java.io.*;
 import java.util.*;

 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.io.*;
 import org.apache.hadoop.mapreduce.*;
 import org.apache.hadoop.mapreduce.lib.output.*;
 import org.apache.hadoop.mapreduce.lib.input.*;
 import org.apache.hadoop.conf.*;
 import org.apache.hadoop.util.*;
 public class Score_Process extends Configured implements Tool {
     /**
      * 程序说明：主要用来实现计算学生的平均成绩。
      * 数据输入：文件形式输入，每一行包含学生姓名 学生成绩。一个学生有多门成绩则有多行。例如：张三 98
      * 数据输出：张三 84 学生姓名 学生平均成绩
      * 实现思路：在map阶段<张三，（98,68,……）>
      * **/

     public static class Map extends Mapper<LongWritable,Text,Text,IntWritable>{
         public void map(LongWritable key,Text value,Context context)throws IOException,InterruptedException{
             String line=value.toString();
             System.out.println(line);//测试
             StringTokenizer tokenizer=new StringTokenizer(line);
             while(tokenizer.hasMoreTokens()){
                 String name=tokenizer.nextToken();
                 String strscore=tokenizer.nextToken();
                 int intscore=Integer.parseInt(strscore);
                 context.write(new Text(name), new IntWritable(intscore));
             }

         }

     }

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

     }

     public int run(String[] args) throws Exception{
         Job job=new Job(getConf());
         job.setJarByClass(Score_Process.class);
         job.setJobName("Score_Process");

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

         job.setMapperClass(Map.class);
         //job.setCombinerClass(Reduce.class);
         job.setReducerClass(Reduce.class);

         job.setInputFormatClass(TextInputFormat.class);
         job.setOutputFormatClass(TextOutputFormat.class);

         FileInputFormat.setInputPaths(job, new Path(args[0]));
         FileOutputFormat.setOutputPath(job, new Path(args[1]));
         boolean success=job.waitForCompletion(true);

         return success?0:1;
     }

     public static void main(String[] args)throws Exception{
         int ret=ToolRunner.run(new Score_Process(), args);
         System.exit(ret);
     }

 }