Creating an in-memory index in Java using a Multimap

gistfile1.java

import java.io.File;
import java.util.regex.Pattern;
import java.util.Scanner;
import com.google.common.collect.ArrayListMultimap;

/** create in-memory mappings from words to the files that contain them */
public class Indexer {
  public static ArrayListMultimap<String,String> buildIndex(String dirName) throws java.io.IOException {
    ArrayListMultimap<String,String> map = ArrayListMultimap.create();
    Pattern p =  Pattern.compile("[\\s#&!:,;\\.\\\\+-]+");
    File dir = new File(dirName);
    for (File f : dir.listFiles()) {
      String contents = new Scanner(f).useDelimiter("\\Z").next();
      for (String word : p.split(contents.toLowerCase())) {
        map.put(word, f.getName());
      }
    }
    return map;
  }

  //for testing
  public static void main(String args[]) throws java.io.IOException {
    ArrayListMultimap<String,String> index = Indexer.buildIndex(args[0]);
    System.out.println(index.get(args[1]));
  }
}