Java and string formatting using mask

Date "11 Mar 2020"

The other day I was working on some ecommerce system. In this part of the app I had to display a barcode in numeric format. The requested design contained something like the following:

1234 12345 12345 1234 1

but I was simply returning a string:

1234123451234512341

Easy peasy lemon squeezy, it’s a 5min job including unit tests. First thought was to use some regexp. You don’t love it? Ew, are you a newbie?! Ok, ok I admit I have a little Stockholm Syndrome. I think the code would look something like:

String s = "1234123451234512341";
s.replaceAll("(.{4})", "$1 ");

Job done! More 9gag time for me! But hey! To easy, something’s fishy here. The pattern showed in design has 4 chars, then 5 chars, 5 chars, 4 chars and a single one. I noticed that when writing unit tests. No way there is some elegant way of achieving this with regexp. I have to find something different.

Then I stumbled upon MaskFormatter. Very handy in my case, where I have to format string using a… mask, duh. The big downside is the fact it is a part of javax.swing.text package. Usually it is used together with JFormattedTextField. But I used it for simple string manipulation.

My final solution was:

MaskFormatter maskFormatter = new MaskFormatter("#### ##### ##### #### #");
maskFormatter.setValueContainsLiteralCharacters(false);
return maskFormatter.valueToString(barcode).trim();

Works like a charm.