倒排索引的分布式实现（MapReduce程序）

package aturbo.index.inverted;


import java.io.IOException;
import java.util.HashSet;


import org.apache.commons.lang3.StringUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;


public class InvertedIndex {


	public static class Map extends Mapper<LongWritable, Text, Text, Text>{
		private Text documentId;
		private Text word = new Text();
		
		@Override
		protected void setup(Context context){
			String filename = ((FileSplit)context.getInputSplit()).getPath().getName();
			documentId = new Text(filename);
		}
		
		@Override
		protected void map(LongWritable key,Text value,Context context)throws IOException,InterruptedException{
			for(String token:StringUtils.split(value.toString())){
				word.set(token);
				context.write(word, documentId);
			}
		}
	}
	
	public static class Reduce extends Reducer<Text, Text, Text, Text>{
		
		private Text docIds = new Text();
		public void reduce(Text key,Iterable<Text> values,Context context)throws IOException,InterruptedException{
			HashSet<Text> uniqueDocIds = new HashSet<Text>();
			for(Text docId:values){
				uniqueDocIds.add(docId);
			}
			docIds.set(new Text(StringUtils.join(uniqueDocIds, ",")));
			context.write(key, docIds);
		}
	}
	
	public static void main(String[] args)throws Exception{
		Configuration conf = new Configuration();
		
		String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
		if(otherArgs.length!=2){
			System.err.println("Usage:InvertedIndex<in><out>");
			System.exit(2);
		}
		
		Job job = new Job(conf,"inverted index");
		job.setJarByClass(InvertedIndex.class);
		job.setMapperClass(Map.class);
		job.setCombinerClass(Reduce.class);
		job.setReducerClass(Reduce.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(Text.class);
		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
		System.exit(job.waitForCompletion(true)?0:1);
	}
}