Java password validation regex

Question

We have password requirements:

Must contain capital letters
Must contain lowercase letters
Must contain numbers
Must contain special characters
There should be no characters repeating one after another

Now our validation regex is:

^((?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[!@#$%&*]))

So it doesn't validating the 5th requirement.

How to improve regex to validate characters repeating?

Honestly, wouldn't this be easier and more readable with a loop? — phipsgabler
– phipsgabler, Commented Feb 3, 2023 at 12:57
We are using it for validating HTTP method body with @Pattern annotation on the field — Montana
– Montana, Commented Feb 3, 2023 at 15:12

The fourth bird · Accepted Answer · 2023-02-03 07:50:30Z

1

You can remove the outer capture group, and then use a negative lookahead with a backreference to group 1 to exclude 2 repeating characters on after another.

^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[!@#$%&*])(?!.*(.)\1)

In Java

String regex = "^(?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[!@#$%&*])(?!.*(.)\\1)";

Regex demo

Note that if using the pattern only for a password validation, the minimum length is just 4 characters.

To reduce some backtracking, you could also use negation:

^(?=[^\r\n\d]*\d)(?=[^\r\na-z]*[a-z])(?=[^\r\nA-Z]*[A-Z])(?=[^\r\n!@#$%&*]*[!@#$%&*])(?!.*(.)\1)

Regex demo

edited Feb 3, 2023 at 7:50

answered Feb 3, 2023 at 7:45

The fourth bird

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