Solution to Inverted Index Code

The following source code implements a solution to the inverted indexer problem posed at the checkpoint. The source code is structurally very similar to the source for Word Count; only a few lines really need to be modified.

import java.io.IOException;
import java.util.Iterator;
import java.util.StringTokenizer;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.FileInputFormat;
import org.apache.hadoop.mapred.FileOutputFormat;
import org.apache.hadoop.mapred.FileSplit;
import org.apache.hadoop.mapred.JobClient;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;

public class LineIndexer {

public static class LineIndexMapper extends MapReduceBase
implements Mapper {

private final static Text word = new Text();
private final static Text location = new Text();

public void map(LongWritable key, Text val,
OutputCollector output, Reporter reporter)
throws IOException {

FileSplit fileSplit = (FileSplit)reporter.getInputSplit();
String fileName = fileSplit.getPath().getName();
location.set(fileName);

String line = val.toString();
StringTokenizer itr = new StringTokenizer(line.toLowerCase());
while (itr.hasMoreTokens()) {
word.set(itr.nextToken());
output.collect(word, location);
}
}
}



public static class LineIndexReducer extends MapReduceBase
implements Reducer {

public void reduce(Text key, Iterator values,
OutputCollector output, Reporter reporter)
throws IOException {

boolean first = true;
StringBuilder toReturn = new StringBuilder();
while (values.hasNext()){
if (!first)
toReturn.append(", ");
first=false;
toReturn.append(values.next().toString());
}

output.collect(key, new Text(toReturn.toString()));
}
}


/**
* The actual main() method for our program; this is the
* "driver" for the MapReduce job.
*/
public static void main(String[] args) {
JobClient client = new JobClient();
JobConf conf = new JobConf(LineIndexer.class);

conf.setJobName("LineIndexer");

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

FileInputFormat.addInputPath(conf, new Path("input"));
FileOutputFormat.setOutputPath(conf, new Path("output"));

conf.setMapperClass(LineIndexMapper.class);
conf.setReducerClass(LineIndexReducer.class);

client.setConf(conf);

try {
JobClient.runJob(conf);
} catch (Exception e) {
e.printStackTrace();
}
}
}