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?

Solution 1

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

Try replaceAll.

Solution 2

Use replaceAll over replace

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