Regex for checking alphabets and numbers in a localized string

Question

I have an input field that is localized . I need to add validation with a regular expression that should only accept alphabets and numbers. I could use [a-z0-9] if I only used English.

I am currently using the Character.isLetterOrDigit(name.charAt(i)) method (yes, I repeat through each character) to filter out alphabets present in different languages.

Are there any better ways to do this? Are any regular expressions or other libraries available for this?

Answer 1

Starting with 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"); } 

without an option, it does not recognize the word "Müller", but using Pattern.UNICODE_CHARACTER_CLASS

Includes a Unicode version of the predefined character classes and POSIX character classes.

See details

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

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

See tchrist ’s famous answer about Java regex warnings, including an update of what has changed with Java 7 (from this will be in Java 8)

Answer 2

 boolean foundMatch = name.matches("[\\p{L}\\p{Nd}]*"); 

must work.

[\p{L}\p{Nd}] matches a character that is a Unicode letter or number. The regex .matches() method ensures that the entire string matches the pattern.

Answer 3

Some people, faced with a problem, think: "I know, I will use regular expressions." Now they have two problems.

- Jamie Zawinki

I say this as a joke, but repeating through String, as you do, will have runtime performance, at least as good as any regular expression - there is no way that the regular expression can do what you want faster; and you don’t have the overhead of compiling the template in the first place.

Until:

• to check, you do not need to do anything else similar to a regular expression (nothing was mentioned in the question)
• the intent of the loop passing through String becomes clear (and if not, refactor until it is)

then why replace it with regex just because you can?