Java Regex to mask alphanumeric string and show last 4 digits

Question

I have an input string that looks like any of the following:

Z43524429
46D92S429
3488DFJ33

Basically the string can contain alphabet characters or digits. However it cannot contain symbols, just letters and numbers. I would like to mask it so that it looks like this:

*****4429
*****S429
*****FJ33

I've looked everywhere to find an java code example that uses regex to mask this. I've found this post on stack but that assumes that the input is purely a number.

I adjusted the regex to /\w(?=\w{4})/g to include characters as well. It seems to work here. But when I try to implement it in java it doesn't work. Here's the line in my java code:

String mask = accountNumber.replace("\\w(?=\\w{4})", "*");

The mask ends up being the same as the accountNumber. So obviously the regex is not working. Any thoughts?

If the string has always the same format, you don't need a regex. Build a new string that starts with five `*` and ends with the four last characters of the original string. — Casimir et Hippolyte, Oct 08 '15 at 18:41
Thanks for the question BTW. Because of that I found Regex for String masking. Very Helpful.. — Jigar, Jun 07 '17 at 05:37

score 5 · Accepted Answer · answered Oct 08 '15 at 18:00

5

You're using replace, which doesn't use regular expressions.

Try replaceAll.

answered Oct 08 '15 at 18:00

super_aardvark

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score 1 · Answer 2 · edited Sep 01 '20 at 13:15

1

Use replaceAll over replace

String mask = accountNumber.replaceAll("\\w(?=\\w{4})", "*");

edited Sep 01 '20 at 13:15

IQbrod

2,060
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answered Sep 01 '20 at 11:42

Kapil Ghuman

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Java Regex to mask alphanumeric string and show last 4 digits

2 Answers2