code: private final String getNotOverridableContent() throws IOException {
  
  		if (Files.exists(filePath)) {
  			List<String> lines = Files.readAllLines(filePath,
  					fileType.getEncoding());
  			boolean isNotOverridable = false;
  			StringWriter notOverridableContentWriter = new StringWriter();
  			for (String line : lines) {
  				if (line.contains(fileType.getSpecificCodeStartMark())) {
  					isNotOverridable = true;
  				} else if (line.contains(fileType.getSpecificCodeEndMark())) {
  					isNotOverridable = false;
  				} else {
  					if (isNotOverridable) {
  						notOverridableContentWriter.append(line + SKIP_LINE);
  					}
  				}
  			}
  			return notOverridableContentWriter.toString();
  		}
  		return "";
  	}
docs: extract non generated content from a file to keep it after next generation
  @return
  @throws IOException