Write an empty MapReduce job

Question

I want to write an empty mapreduce job, Actually I mean a mapreduce job that doing nothing, Just has a Mapper, a Reducer and a main class. I want it for a test in hortonwoks sandbox 2.1. this is my code:

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

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.util.*;

public class MainClassName {

  public static class Map extends MapReduceBase 
    implements Mapper<IntWritable, Text, IntWritable, Text> 
  {
    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();

    public void map(LongWritable key, Text value, 
      OutputCollector<Text, IntWritable> output, 
      Reporter reporter) throws IOException 
    {
      output.collect(word, one);
    }
  }

  public static class Reduce extends MapReduceBase 
    implements Reducer<Text, IntWritable, Text, IntWritable> 
  {
    public void reduce(Text key, Iterator<IntWritable> values, 
      OutputCollector<Text, IntWritable> output, Reporter reporter) 
      throws IOException 
    {
      int data = 0;
      }
      output.collect(key, new IntWritable(data));
    }
  }

  public static void main(String[] args) throws Exception 
  {
    JobConf conf = new JobConf(MainClassName.class);
    conf.setJobName("JobName");

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

    conf.setMapperClass(Map.class);
    conf.setCombinerClass(Reduce.class);
    conf.setReducerClass(Reduce.class);

    conf.setInputFormat(TextInputFormat.class);
    conf.setOutputFormat(TextOutputFormat.class);

    FileInputFormat.setInputPaths(conf, new Path(args[0]));
    FileOutputFormat.setOutputPath(conf, new Path(args[1]));

    JobClient.runJob(conf);
  }
}

Is it correct? but it gives me an error:

Description Resource Path Location Type The type MainClassName.Map must implement the inherited abstract method Mapper.map(Text, Text, OutputCollector, Reporter) MainClassName.java /mainempty/src line 14 Java Problem

And also I want to know which java files must be imported to run a simple job. Thanks a lot. :)

Answer 1

Your type arguments are a bit muddled. Your mapper is taking a <LongWritable,Text> pair, and outputting a <Text,IntWritable> pair. However your class declaration says:

implements Mapper<IntWritable, Text, IntWritable, Text> 

Which should read

implements Mapper<LongWritable, Text, Text, LongWritable>

The rest looks OK.