java - Regex for validating alphabetics and numbers in the localized string

Question

I have an input field which is localized. I need to add a validation using a regex that it must take only alphabets and numbers. I could have used [a-z0-9] if I were using only English.

As of now, I am using the method Character.isLetterOrDigit(name.charAt(i)) (yes, I am iterating through each character) to filter out the alphabets present in various languages.

Are there any better ways of doing it? Any regex or other libraries available for this?

Answer 1

Since Java 7 you can use Pattern.UNICODE_CHARACTER_CLASS

String s = "Müller";

Pattern p = Pattern.compile("^\w+$", Pattern.UNICODE_CHARACTER_CLASS);
Matcher m = p.matcher(s);
if (m.find()) {
    System.out.println(m.group());
} else {
    System.out.println("not found");
}

with out the option it will not recognize the word "Müller", but using Pattern.UNICODE_CHARACTER_CLASS

Enables the Unicode version of Predefined character classes and POSIX character classes.

See here for more details

You can also have a look here for more Unicode information in Java 7.

and here on regular-expression.info an overview over the Unicode scripts, properties and blocks.

See here a famous answer from tchrist about the caveats of regex in Java, including an updated what has changed with Java 7 (of will be in Java 8)