How to have a proper JTextField IP address in Java?

Question

First of all, I couldn't find any of my question on google.
This is the following code that I used.

ipAddress = new MaskFormatter("###.###.###.###");
JTextField txtAddress = new JFormattedTextField(ipAddress);

But the code above gives user to (must) input exactly 12 characters.
How to make the JTextField can be written as "12.10.25.25" ?

Answer 1

I would do it differently:

Simply wait for the user to somehow confirm that he has finished entering the address (for example by observing when the field looses focus) and retrieve the value of the field and use one of the many regular expressions that check all properties of valid ip addresses.

Looking at the Oracle tutorial here it seems to me that using a JTextFormattedTextField simply is the wrong answer. That class and the corresponding formats are for either locale-based formatting of dates or numbers.

I think you should be rather looking into input validation; see here for details; and as said; your validation could be based on the things you find here.

Finally: the point is to come up with a consistent user experience. Dont put yourself into a corner by saying: I saw this approach; so I absolutely must use that type of component. Instead, check out the possible options, and go for that one that (given your "budget" of development resources) gives the user the best experience.

Example: instead of using 1 JFormattedTextField, you could go for 4 textfields, and even write code that would move the focus automatically forth and back. Many things are possible; it only depends on how much time you are willing to spend.

Answer 2

My homegrown IP address control based on a single JTextField

import javax.swing.*;
import javax.swing.text.DefaultEditorKit;
import java.awt.*;
import java.awt.event.*;
import java.net.InetAddress;
import java.net.UnknownHostException;

public class JIp4AddressInput extends JTextField
{
    private final char[] buff = "  0.  0.  0.  0".toCharArray();

    private int bpos;

    private void putnum (int num, int offset)
    {
        int a = num/100;
        num -= a*100;
        int b = num/10;
        num -= b*10;
        buff[offset] = (char)('0'+a);
        buff[offset+1] = (char)('0'+b);
        buff[offset+2] = (char)('0'+num);
    }

    private void align (int base)
    {
        int end = base+3;
        StringBuffer sb = new StringBuffer();
        for (int s=base; s<end; s++)
        {
            if (buff[s] != ' ')
                sb.append(buff[s]);
        }
        while (sb.length() > 1 && sb.charAt(0) == '0')
            sb.delete(0,1);
        while (sb.length() < 3)
            sb.insert(0, ' ');
        try
        {
            int num = Integer.parseInt(sb.toString().trim());
            if (num > 255)
                sb = new StringBuffer("255");
            if (num < 0)
                sb = new StringBuffer("  0");
        }
        catch (NumberFormatException e)
        {
            sb = new StringBuffer("  0");
        }
        for (int s=base; s<end; s++)
        {
            buff[s] = sb.charAt(s-base);
        }
    }

    private void alignAll()
    {
        align(0);
        align (4);
        align(8);
        align (12);
    }

    private void fwd ()
    {
        bpos = bpos == 15 ? bpos : bpos +1;
    }

    private void back ()
    {
        bpos = bpos == 0 ? bpos : bpos -1;
    }

    private void backspace()
    {
        back();
        if (bpos == 3 || bpos == 7 || bpos == 11)
        {
            return;
        }
        if (bpos < 15)
            buff[bpos] = ' ';
    }

    private void setChar (char c)
    {
        if (bpos == 3 || bpos == 7 || bpos == 11)
        {
            fwd();
        }
        if (bpos < 15)
            buff[bpos] = c;
        fwd();
    }

    public JIp4AddressInput()
    {
        super();
        setPreferredSize(new Dimension(110, 30));
        setEditable(false);

        Action beep = getActionMap().get(DefaultEditorKit.deletePrevCharAction);
        beep.setEnabled (false);

        setText (new String (buff));

        addFocusListener(new FocusListener()
        {
            @Override
            public void focusGained(FocusEvent e)
            {
                setText (new String (buff));
                setCaretPosition(0);
                getCaret().setVisible(true);
            }

            @Override
            public void focusLost(FocusEvent e)
            {
                alignAll();
                setText(new String(buff));
            }
        });

        addKeyListener(new KeyAdapter()
        {
            @Override
            public void keyTyped (KeyEvent e)
            {
                bpos = getCaretPosition();
                char c = e.getKeyChar();
                if ((c>= '0' && c<= '9') || c == ' ')
                {
                    setChar (c);
                }
                else if (c == KeyEvent.VK_BACK_SPACE)
                {
                    backspace();
                }
                else if (c == KeyEvent.VK_ENTER)
                {
                    alignAll();
                }
                setText(new String(buff));
                setCaretPosition(bpos);
            }
        });
    }

    ////////////////////////////////////////////////////////////////////////////////////////

    public InetAddress getAddress()
    {
        String[] parts = new String(buff).split("\\.");
        byte[] adr = new byte[4];
        for (int s=0; s<4; s++)
            adr[s] = (byte)Integer.parseInt(parts[s].trim());
        try {
            return InetAddress.getByAddress(adr);
        } catch (UnknownHostException e) {
            return null;
        }
    }

    public void putAddress (InetAddress in)
    {
        byte[] adr = in.getAddress();
        putnum(adr[0]&0xff, 0);
        putnum(adr[1]&0xff, 4);
        putnum(adr[2]&0xff, 8);
        putnum(adr[3]&0xff, 12);
        alignAll();
        setText (new String(buff));
    }
}