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Accepted
omaza1990
Asked: 2020-03-29 15:21:33 +0800 CST 2020-03-29 15:21:33 +0800 CST

Validate ID in Java

  • 772

How to validate a field jTextFieldwith the format-pattern of a DNI? Example: 72033197V

The pattern must have: 8 numbers + 1 letter (12345678A).

I have programmed the following code to validate a DNIand it works. Is it the correct way of validation?

Test code:

import java.util.regex.*;
import java.util.Scanner;

public class validarDNI {
    public static void main(String[] args) {
        String dniIntroducido = null;
        Scanner miScanner = new Scanner(System.in);
        Pattern patron = Pattern.compile("[0-9]{7,8}[A-Z a-z]");
        System.out.print("Introduce un DNI correcto: ");
        dniIntroducido = miScanner.nextLine();
        Matcher mat = patron.matcher(dniIntroducido);
        while(!mat.matches()){
           System.out.println("El DNI introducido es incorrecto, por favor introduzca un DNI válido.");
           System.out.print("Introduce un DNI correcto: ");
           dniIntroducido = miScanner.nextLine();
           mat = patron.matcher(dniIntroducido);
        }
        System.out.println("El DNI " + dniIntroducido + " es válido.");
    }
}

Well, my problem comes when importing it in a jTextFieldto verify that it has 8 numbers and a single letter. And that when typing the letter it becomes uppercase ( toUpperCase()).

He jTextFieldis called: jTextField_DNI.

I have created an event private void textfield_DNIKeyPressed(java.awt.event.KeyEvent evt) {so that it checks character by character but... How do I implement it in the jTextField?

private void textfield_DNIKeyPressed(java.awt.event.KeyEvent evt) {

}
java

2 Answers

  1. Best Answer

    The problem that you are going to have when checking character by character is that if you validate each time the user enters a character, the first 7 will result in "DNI no válido"even if everything is being written correctly. The most recommended thing is that you validate when it JTextFieldloses focus, or when the user hits save, next, or any button to continue.

    To validate when it loses focus you add an FocusListenerto JTextFieldand implement the method focusLost:

    jTextField_DNI.addFocusListener(new FocusListener() {
    @Override
    public void focusGained(FocusEvent e) {

    }

    @Override
    public void focusLost(FocusEvent e) {
        String text = jTextField_DNI.getText();
        if(text != null) {
            // Valida text aquí
        }
    }
});

    Or if you want character by character then add a KeyListenerto JTextFieldand choose one of the 3 methods to implement the logic you want:

    jTextField_DNI.addKeyListener(new KeyListener() {
    @Override
    public void keyTyped(KeyEvent e) {
        String text = jTextField_DNI.getText();
        if(text != null) {
            // Valida text aquí
        }
    }

    @Override
    public void keyPressed(KeyEvent e) {

    }

    @Override
    public void keyReleased(KeyEvent e) {

    }
});
    • 1 
  2. private final String dniChars="TRWAGMYFPDXBNJZSQVHLCKE";   
 private boolean validarDNI(String itDNI) {
            String intPartDNI = itDNI.trim().replaceAll(" ", "").substring(0, 7);
            char ltrDNI = itDNI.charAt(8);
            int valNumDni = Integer.parseInt(intPartDNI) % 23;
            if (itDNI.length()!= 9 && isNumeric(intPartDNI) == false && dniChars.charAt(valNumDni)!= ltrDNI) {
                return false;
            } else {
                return true;
            }
            
        }

    With this method you validate if the letter is correct for the numeric part, as you know the module of the numeric part (8 digits) of 23, responds to a letter that corresponds to a Character of the string dniChars

    • 0