Regular expression for validation

Question

I need to verify a password string by using Java. This is the requirement of validation:

• at least 1 number
• at least 1 alphabet character
• at least 1 character from set !@#$%^&*()_+=-~`][{};':"/.>?,<
• 8 to 20 characters

After screwing around and banging my head to the wall several times, I came up with this regular expression

if (!password.matches("^(?=.+[0-9])(?=.+[a-zA-Z])(?=.+[\\x21-\\x2F\\x3A-\\x40\\x5B-\\x60\\x7B-\\x7E])[0-9a-zA-Z\\x21-\\x2F\\x3A-\\x40\\x5B-\\x60\\x7B-\\x7E]{8,20}$")) {

}

which looks too awful and insane. Is there any better way to achieve this mission ?

Answer 1

I recommend using the regular expressions for what they do best, but using code for things that the regexp doesn't do well. Something like this. (Sorry, I haven't tested this code, but it should give the idea even if I made a mistake and it won't run.)

Pattern special_chars = Pattern.compile("[!@#$%^&*()_+=-~`\][{};':\"/.>?,<]");
Pattern number_chars = Pattern.compile("[0-9]");
Pattern letter_chars = Pattern.compile("[a-zA-Z]");

boolean valid;

valid = (special_chars.matcher(password).find() &&
        number_chars.matcher(password).find() &&
        letter_chars.matcher(password).find() &&
        8 <= password.length() && password.length() <= 20);

Answer 2

With guava CharMatcher .

// at least 1 number
CharMatcher.inRange('0', '9').countIn(password) >= 1 && 
// at least 1 alphabet character
CharMatcher.inRange('a', 'z').or(inRange('A', 'Z')).countIn(password) >= 1 && 
// at least 1 character from set !@#$%^&*()_+=-~`][{};':"/.>?,<
CharMatcher.anyOf("!@#$%^&*()_+=-~`][{};':\"/.>?,<").countIn(password) >= 1 && 
// 8 to 20 characters
password.length() >= 8 && password.length() <= 20

this assumes you want latin alphabet

Answer 3

i believe this has already been answered.

Regular Expression for password validation

but may i suggest that you split up the validation into the respective categories? this way it may be easier and you will be able to tell the user exactly what they're missing.