JavaFX - Use DatePicker custom "format"

CustomDatePicker.java

public class Project_formController implements Initializable, LimitText {

	private static final Logger logger = LoggerFactory.getLogger(Project_formController.class);
	@FXML
	private TextField tf_projNM;
	@FXML
	private DatePicker proj_SDT;
	@FXML
	private DatePicker proj_EDT;
	@FXML
	private TextField tf_status;
	@FXML
	private Button btn_ok;
	@FXML
	private Button btn_reset;
	@FXML
	private TextArea ta_desc;
	private String uid;
	

	public void setUid(String uid) {
		this.uid = uid;
	}

	public String getUid() {
		return uid;
	}

	@FXML
	public void storeAction(ActionEvent event) {
		try {
			createProjectInfo();
		} catch (Exception e) {
			logger.debug("store Action================");
			e.printStackTrace();
		}
	}

	@FXML
	public void clearAction(ActionEvent event) {
		try {
			clearText();
		} catch (Exception e) {
			logger.debug("clearAction==================");
			e.printStackTrace();
		}
	}



	@Override
	public void initialize(URL location, ResourceBundle resources) {
		setDatePicker(proj_SDT);
		setDatePicker(proj_EDT);
	}
	
	public static void setDatePicker(DatePicker picker) {
		 
		String pattern = "yyyyMMdd";
		picker.setPromptText(pattern.toLowerCase());
		picker.setConverter(new StringConverter<LocalDate>() {
			DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(pattern);

			@Override
			public String toString(LocalDate date) {
				if (date != null)
					return dateTimeFormatter.format(date);
				else {
					return "";
				}
			}

			@Override
			public LocalDate fromString(String string) {
				if (string != null && !string.isEmpty()) {
					return LocalDate.parse(string, dateTimeFormatter);
				} else {
					return null;
				}
			}
		});
		picker.setEditable(false);
	}
}