How to validate username and password on Android using Java regex?

Question

I need the following regex pattern to validate a username and a password :

Username :

Between 3 and 25 characters
At least one character [a-zA-Z]
Any character such as : 0-9, a-z, A-Z, _

i have ended up with this pattern but i can't figure out how to set the {3,25} (my tests are not validating it yet) :

^[a-zA-Z0-9_]*[a-zA-Z][a-zA-Z0-9_]*{3,25}$

Password :

     * ^                 # start-of-string
     * (?=.*[0-9])       # a digit must occur at least once
     * (?=.*[a-z])       # a lower case letter must occur at least once
     * (?=.*[A-Z])       # an upper case letter must occur at least once
     * (?=.*[a-zA-Z])    # any letter upper or lower case
     * (?=.*[@#$%^&+=])  # a special character must occur at least once
     * (?=\\S+$)          # no whitespace allowed in the entire string
     * .{6,}             # anything, at least six places though
     * $                 # end-of-string
     */
    private Pattern VALID_PASSWORD = Pattern.compile("^(?=.*[0-9])(?=.*[a-z])(?=.*[A-Z])(?=.*[a-zA-Z])(?=.*[@#$%^&+!?=])(?=\\S+$).{6,}$");

I just need to change this pattern to allow special characters but i don't want to make them mandatory.

You could use the same mechanism like (?=.{3,25}$) Or match \S{3,25} — The fourth bird
– The fourth bird, Commented Jun 13, 2020 at 15:34
I need to allow numbers and i want to prevent the user from putting only numbers. So any letter must appear at least once upper or lower, and the whole thing must have between 3 and 25 characters — Tom3652
– Tom3652, Commented Jun 13, 2020 at 15:47

JvdV · Accepted Answer · 2020-06-13 16:08:39Z

3

^Username:

Looking at your current patterns it seems like you can use the following pattern to validate your usernames:

^(?=.*[a-zA-Z])\w{3,25}$

See the Online Demo.

^ - Start string ancor.
(?=.*[a-zA-Z]) - A positive lookahead, for any character other than newline zero or more times followed by a letter within [a-zA-Z] character class.
\w{3,25} - Any character in the class [a-zA-Z0-9_], three times up to a maximum of 25.
$ - End string ancor.

^Password:

When you have checked for at least a single lower and a single upper case letter, that would defeat the purpose of checking any upper or lower case letter later down the line in your current pattern. Also, . which is any character would match special characters like the ones in your character class [@#$%^&+!?=]. When you don't want these to be mandatory, don't use them in a positive lookahead. Instead maybe try the following:

^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])\S{6,}$

The only mandatory characters now are at least one digit, at least one lower case letter and at least one upper case letter. See the Online Demo.

^ - Start string ancor.
(?=.*\d) - Positive lookahead for any character other than newline zero or more times followed by a digit.
(?=.*[a-z]) - Positive lookahead for any character other than newline zero or more times followed by a lower case letter.
(?=.*[A-Z]) - Positive lookahead for any character other than newline zero or more times followed by a upper case letter.
\S{6,} - Any non-whitespace character.
$ - End string ancor.

edited Jun 13, 2020 at 16:08

answered Jun 13, 2020 at 15:50

JvdV

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2 Comments

Tom3652 Over a year ago

Thanks for the explanations. is it the \d making at least one digit mandatory ? It's indeed working fine thank you

JvdV Over a year ago

@TommyD, that is correct. It's shorthand for [0-9], whilst \w is shorthand for [a-zA-Z0-9_]

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