code: public String getRelativeName() {
  		File folder = this.sourceFolder.getAbsoluteFile();
  		File file = this.file.getAbsoluteFile();
  		String folderName = StringUtils.cleanPath(folder.getPath());
  		String fileName = StringUtils.cleanPath(file.getPath());
  		Assert.state(fileName.startsWith(folderName), () -> "The file " + fileName
  				+ " is not contained in the source folder " + folderName);
  		return fileName.substring(folderName.length() + 1);
  	}
docs: Return the name of the file relative to the source folder.
  @return the relative name