code: private String validateFiles(String files, Configuration conf) throws IOException  {
      if (files == null) 
        return null;
      String[] fileArr = files.split(",");
      String[] finalArr = new String[fileArr.length];
      for (int i =0; i < fileArr.length; i++) {
        String tmp = fileArr[i];
        String finalPath;
        Path path = new Path(tmp);
        URI pathURI =  path.toUri();
        FileSystem localFs = FileSystem.getLocal(conf);
        if (pathURI.getScheme() == null) {
          //default to the local file system
          //check if the file exists or not first
          if (!localFs.exists(path)) {
            throw new FileNotFoundException("File " + tmp + " does not exist.");
          }
          finalPath = path.makeQualified(localFs).toString();
        }
        else {
          // check if the file exists in this file system
          // we need to recreate this filesystem object to copy
          // these files to the file system jobtracker is running
          // on.
          FileSystem fs = path.getFileSystem(conf);
          if (!fs.exists(path)) {
            throw new FileNotFoundException("File " + tmp + " does not exist.");
          }
          finalPath = path.makeQualified(fs).toString();
          try {
            fs.close();
          } catch(IOException e){};
        }
        finalArr[i] = finalPath;
      }
      return StringUtils.arrayToString(finalArr);
    }
docs: takes input as a comma separated list of files
  and verifies if they exist. It defaults for file:///
  if the files specified do not have a scheme.
  it returns the paths uri converted defaulting to file:///.
  So an input of  /home/user/file1,/home/user/file2 would return
  file:///home/user/file1,file:///home/user/file2
  @param files
  @return