code: public static int getChunkId(String fileName) {
          Pattern pattern = Pattern.compile("_[\\d]+\\.");
          Matcher matcher = pattern.matcher(fileName);
  
          if(matcher.find()) {
              return new Integer(fileName.substring(matcher.start() + 1, matcher.end() - 1));
          } else {
              throw new VoldemortException("Could not extract out chunk id from " + fileName);
          }
      }
docs: Returns the chunk id for the file name
  
  @param fileName The file name
  @return Chunk id