mao/reduce实现求平均值

 1 import java.io.*;

 2 import java.util.*;

 3 

 4 import org.apache.hadoop.fs.Path;

 5 import org.apache.hadoop.io.*;

 6 import org.apache.hadoop.mapreduce.*;

 7 import org.apache.hadoop.mapreduce.lib.output.*;

 8 import org.apache.hadoop.mapreduce.lib.input.*;

 9 import org.apache.hadoop.conf.*;

10 import org.apache.hadoop.util.*;

11 public class Score_Process extends Configured implements Tool {

12     /**

13      * 程序说明：主要用来实现计算学生的平均成绩。

14      * 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

15      * 数据输出：张三 84 学生姓名 学生平均成绩

16      * 实现思路：在map阶段<张三，（98,68,……）>

17      * **/

18     

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

20         public void map(LongWritable key,Text value,Context context)throws IOException,InterruptedException{

21             String line=value.toString();

22             System.out.println(line);//测试

23             StringTokenizer tokenizer=new StringTokenizer(line);

24             while(tokenizer.hasMoreTokens()){

25                 String name=tokenizer.nextToken();

26                 String strscore=tokenizer.nextToken();

27                 int intscore=Integer.parseInt(strscore);

28                 context.write(new Text(name), new IntWritable(intscore));

29             }

30             

31         }

32         

33     }

34     

35     public static class Reduce extends Reducer<Text,IntWritable,Text,IntWritable>{

36         public void reduce(Text key,Iterable<IntWritable>values,Context context) throws IOException, InterruptedException{

37             int sun=0,count=0;

38             for(IntWritable val:values){

39                 sun+=val.get();

40                 count++;

41             }

42             int averscore=(int)sun/count;

43             context.write(key, new IntWritable(averscore));

44         }

45         

46     }

47     

48     public int run(String[] args) throws Exception{

49         Job job=new Job(getConf());

50         job.setJarByClass(Score_Process.class);

51         job.setJobName("Score_Process");

52         

53         job.setOutputKeyClass(Text.class);

54         job.setOutputValueClass(IntWritable.class);

55         

56         job.setMapperClass(Map.class);

57         //job.setCombinerClass(Reduce.class);

58         job.setReducerClass(Reduce.class);

59         

60         job.setInputFormatClass(TextInputFormat.class);

61         job.setOutputFormatClass(TextOutputFormat.class);

62         

63         FileInputFormat.setInputPaths(job, new Path(args[0]));

64         FileOutputFormat.setOutputPath(job, new Path(args[1]));

65         boolean success=job.waitForCompletion(true);

66         

67         return success?0:1;

68     }

69     

70     public static void main(String[] args)throws Exception{

71         int ret=ToolRunner.run(new Score_Process(), args);

72         System.exit(ret);

73     }

74 

75 }