MaskFormatter with variable length

Question

I'm trying to create a MaskFormatter with the following mask:
"AAAA AAAA AAAA AAAA"
The user should be able to enter whatever he likes as long as it is automatically formatted with a space between each group.
Valid combinations are:
1234 45
12
FF12 5454 546
etc...
Further on, small letters should be converted to Uppercase when typing. How do I do this?
I have already tried to write a custom VariableMaskFormatter as described in (http://forum.java.sun.com/thread.jspa?forumID=57&threadID=461577&start=3)
but I doesn't work as expected.
It only works if the placeholdercharacter which is used is also an allowed charachter when typing. But I don't want to make the space character an allowed character.
How can this be solved?
Thanks
Fabian

Answer 1

Thank you. I have been able to create a custom MaskFormatter which will dynamically adapt the mask based on what was entered.
But I still have two open issues:
1. How can I do so that all smaller letters are converted to captital letters when typing? Normally you would use the letter "U" in the mask, but, users should be able to enter a alphanumeric character, so I use "A" instead.
2. Cursor problem:
- How can I make delete and backspace button act as if it was in a notepad? If I press delete, charachters at the right from the cursor should be deleted and the cursor should not move forward.
Please find below some code samples.
package test.component;
import java.text.ParseException;
import javax.swing.text.MaskFormatter;
public class VariableLengthMaskFormatter extends MaskFormatter {
    public VariableLengthMaskFormatter() {
        super();
    public VariableLengthMaskFormatter(String mask) throws ParseException {
        super( mask );
     * Override the setMask method
    public void setMask(String mask) throws ParseException {
        super.setMask(mask);
     * Update our blank representation whenever the mask is updated.
    public void setPlaceholderCharacter(char placeholder) {
      super.setPlaceholderCharacter(placeholder);
    /* (non-Javadoc)
     * @see javax.swing.text.MaskFormatter#stringToValue(java.lang.String)
    public Object stringToValue( String value ) throws ParseException {
        Object rv;
        // Get the mask
        String mask = getMask();
        if ( mask != null ) {
            // Change the mask based upon the string passed in
            setMask( getMaskForString( mask, value ) );
            // Using the substring of the given string up to the mask length,
            // convert it to an object
            rv = super.stringToValue( value.substring( 0, getMask().length() ) );
            // Change mask back to original mask
            setMask( mask );
        } else
            rv = super.stringToValue( value );
        // Return converted value
        return rv;
     * Answer what the mask should be for the given string based on the
     * given mask. This mask is just the subset of the given mask up to
     * the length of the given string or where the first placeholder
     * character occurs in the given string. The underlying assumption
     * here is that the given string is simply the text from the
     * formatted field upon which we are installed.
     * @param value The string for which to determine the mask
     * @return A mask appropriate for the given string
    protected String getMaskForString( String mask, String value ) {
        StringBuffer sb = new StringBuffer();
        int maskLength = mask.length();
        char placeHolder = getPlaceholderCharacter();
        for (int k = 0, size = value.length(); k < size && k < maskLength ; k++) {
            if ( placeHolder == value.charAt( k ) ) {
                //break;
                sb.append(' ');               
            } else {
                sb.append( mask.charAt( k ) );
        return sb.toString();
         MaskFormatter theRekFormat = null;
         try {
             theRekFormat = new VariableLengthMaskFormatter( "AAAA AAAA AAAA AAAA" );
             theRekFormat.setPlaceholderCharacter(' ');
             theRekFormat.setValueContainsLiteralCharacters( false);
         } catch (Exception ex) {
             System.out.println(ex.toString());
         JFormattedTextField myMaskAccount = new JFormattedTextField(theRekFormat);
          myMaskAccount.addKeyListener(new KeyAdapter(){
                        public void keyReleased(KeyEvent ke){
                          if(ke.getKeyCode() == KeyEvent.VK_DELETE) {
                              myMaskAccount.setCaretPosition(myMaskAccount.getCaretPosition()-1);
                          } else {
                              System.out.println("listening to key: " + ke.getKeyCode());
                          }}});