Mask Formatter in Java

The Java 2 Standard Edition (J2SE), version 1.4 add the Swing component JFormattedTextField. With this component it's possible build formatted fields like telephone, date, CPF, etc...

The DefaultFormatterFactory component comes with preinstalled formatters for dates, numbers, java.text.Format subclasses.

Configuring acceptable input

Masked input is typically configured by using an instance of the MaskFormatter class. Found in the javax.swing.text package, MaskFormatter works by using a series of characters to designate acceptable input. Each of the eight characters in the series represents one character in the input, as listed below:

# - A number
? - A letter
A - A letter or number
* - Anything
U - A letter, with lowercase characters mapped to their uppercase equivalents
L - A letter, with uppercase characters mapped to their lowercase equivalents
H - A hexadecimal digit (A-F, a-f, 0-9)
' - Used to escape another mask character

In addition to MaskFormatter, you can use the DateFormat and NumberFormat classes from the java.text package to specify the input format. Listing 1 shows some possible formats.

// Four-digit year, followed by month name and day of month,
// each separated by two dashes (--)
DateFormat format =
new SimpleDateFormat("yyyy--MMMM--dd");
DateFormatter df = new DateFormatter(format);
// US Social Security number
MaskFormatter mf1 =
new MaskFormatter("###-##-####");
// US telephone number
MaskFormatter mf2 =
new MaskFormatter("(###) ###-####");


Once you've specified the input format, you would then pass the formatter into the JFormattedTextField constructor, as shown below:

JFormattedTextField ftf1 = new
JFormattedTextField(df);

Depending on the formatter used, there are other configurable options. For instance, with MaskFormatter, you can set the placeholder character with setPlaceholderCharacter(char). Also, for date fields, it helps if you initialize the field to some value so a user will know what input format is acceptable.


Example:

import java.awt.*;
import javax.swing.*;
import javax.swing.text.*;
import java.util.*;
import java.text.*;
public class FormattedSample {
public static void main (String args[]) throws ParseException {
JFrame f = new JFrame("JFormattedTextField Sample");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container content = f.getContentPane();
content.setLayout(new BoxLayout(content, BoxLayout.PAGE_AXIS));
// Four-digit year, followed by month name and day of month,
// each separated by two dashes (--)
DateFormat format =
new SimpleDateFormat("yyyy--MMMM--dd");
DateFormatter df = new DateFormatter(format);
JFormattedTextField ftf1 = new
JFormattedTextField(df);
ftf1.setValue(new Date());
content.add(ftf1);
// US Social Security number
MaskFormatter mf1 =
new MaskFormatter("###-##-####");
mf1.setPlaceholderCharacter('_');
JFormattedTextField ftf2 = new
JFormattedTextField(mf1);
content.add(ftf2);
// US telephone number
MaskFormatter mf2 =
new MaskFormatter("(###) ###-####");
JFormattedTextField ftf3 = new
JFormattedTextField(mf2);
content.add(ftf3);
f.setSize(300, 100);
f.show();
}
}

Source: IBM, SUN