我尝试在mapreduce中实现简单的分组。
我的输入文件如下：

7369,SMITH,CLERK,800,20
7499,ALLEN,SALESMAN,1600,30
7521,WARD,SALESMAN,1250,30
7566,JONES,MANAGER,2975,20
7654,MARTIN,SALESMAN,1250,30
7698,BLAKE,MANAGER,2850,30
7782,CLARK,MANAGER,2450,10
7788,SCOTT,ANALYST,3000,20
7839,KING,PRESIDENT,5000,10
7844,TURNER,SALESMAN,1500,30
7876,ADAMS,CLERK,1100,20
7900,JAMES,CLERK,950,30
7902,FORD,ANALYST,3000,20
7934,MILLER,CLERK,1300,10

我的Map器类：

public class Groupmapper extends Mapper<Object,Text,IntWritable,IntWritable> {
    @Override
    public void map(Object key, Text value, Context context) throws IOException, InterruptedException{
        String line = value.toString();
        String[] parts=line.split(",");
        String token1=parts[3];
        String token2=parts[4];
        int deptno=Integer.parseInt(token2);
        int sal=Integer.parseInt(token1);
        context.write(new IntWritable(deptno),new IntWritable(sal));
    }    
}

减速器等级：

public class Groupreducer extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
    IntWritable result=new IntWritable();
    public void Reduce(IntWritable key,Iterable<IntWritable> values, Context context) throws IOException, InterruptedException{
        int sum=0;
        for(IntWritable val:values){
            sum+=val.get();
        }
        result.set(sum);
        context.write(key,result);
    }
}

驾驶员等级：

public class Group {
    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
        Configuration conf=new Configuration();
        Job job=Job.getInstance(conf,"Group");
        job.setJarByClass(Group.class);
        job.setMapperClass(Groupmapper.class);
        job.setCombinerClass(Groupreducer.class);
        job.setReducerClass(Groupreducer.class);
        job.setOutputKeyClass(IntWritable.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);         
    }
}

预期输出应为：

10      8750
20      10875
30      9400

但它会打印下面给出的输出。它没有聚合这些值。它就像身份还原剂。

10      1300
10      5000
10      2450
20      1100
20      3000
20      800
20      2975
20      3000
30      1500
30      1600
30      2850
30      1250
30      1250
30      950

减速器功能不正常。