content: package mrdp.ch3;
  
  import java.io.DataInputStream;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.net.URI;
  import java.util.Map;
  import java.util.StringTokenizer;
  
  import mrdp.utils.MRDPUtils;
  
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.filecache.DistributedCache;
  import org.apache.hadoop.fs.FileSystem;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.io.NullWritable;
  import org.apache.hadoop.io.Text;
  import org.apache.hadoop.mapreduce.Job;
  import org.apache.hadoop.mapreduce.Mapper;
  import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
  import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
  import org.apache.hadoop.util.GenericOptionsParser;
  import org.apache.hadoop.util.bloom.BloomFilter;
  import org.apache.hadoop.util.bloom.Key;
  
  public class BloomFilteringDriver {
  
  	public static class BloomFilteringMapper extends
  			Mapper<Object, Text, Text, NullWritable> {
  
  		private BloomFilter filter = new BloomFilter();
  
  		@Override
  		protected void setup(Context context) throws IOException,
  				InterruptedException {
  			URI[] files = DistributedCache.getCacheFiles(context
  					.getConfiguration());
  
  			// if the files in the distributed cache are set
  			if (files != null && files.length == 1) {
  				System.out.println("Reading Bloom filter from: "
  						+ files[0].getPath());
  
  				// Open local file for read.
  				DataInputStream strm = new DataInputStream(new FileInputStream(
  						files[0].getPath()));
  
  				// Read into our Bloom filter.
  				filter.readFields(strm);
  				strm.close();
  			} else {
  				throw new IOException(
  						"Bloom filter file not set in the DistributedCache.");
  			}
  		}
  
  		@Override
  		public void map(Object key, Text value, Context context)
  				throws IOException, InterruptedException {
  
  			// Parse the input into a nice map.
  			Map<String, String> parsed = MRDPUtils.transformXmlToMap(value
  					.toString());
  
  			// Get the value for the comment
  			String comment = parsed.get("Text");
  
  			// If it is null, skip this record
  			if (comment == null) {
  				return;
  			}
  
  			StringTokenizer tokenizer = new StringTokenizer(comment);
  			// For each word in the comment
  			while (tokenizer.hasMoreTokens()) {
  
  				// Clean up the words
  				String cleanWord = tokenizer.nextToken().replaceAll("'", "")
  						.replaceAll("[^a-zA-Z]", " ");
  
  				// If the word is in the filter, output it and break
  				if (cleanWord.length() > 0
  						&& filter.membershipTest(new Key(cleanWord.getBytes()))) {
  					context.write(value, NullWritable.get());
  					break;
  				}
  			}
  		}
  	}
  
  	public static void main(String[] args) throws Exception {
  		Configuration conf = new Configuration();
  		String[] otherArgs = new GenericOptionsParser(conf, args)
  				.getRemainingArgs();
  		if (otherArgs.length != 3) {
  			System.err.println("Usage: BloomFiltering <in> <cachefile> <out>");
  			System.exit(1);
  		}
  
  		FileSystem.get(conf).delete(new Path(otherArgs[2]), true);
  
  		Job job = new Job(conf, "StackOverflow Bloom Filtering");
  		job.setJarByClass(BloomFilteringDriver.class);
  		job.setMapperClass(BloomFilteringMapper.class);
  		job.setNumReduceTasks(0);
  		job.setOutputKeyClass(Text.class);
  		job.setOutputValueClass(NullWritable.class);
  		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
  		FileOutputFormat.setOutputPath(job, new Path(otherArgs[2]));
  
  		DistributedCache.addCacheFile(
  				FileSystem.get(conf).makeQualified(new Path(otherArgs[1]))
  						.toUri(), job.getConfiguration());
  
  		System.exit(job.waitForCompletion(true) ? 0 : 1);
  	}
  }
  