Regex Java allow number, letters, special char (some)

Question

I have a file name, lets say upload 23_3.jpg. I would like to allow only letters, (.) period, (-) hypen sign, underscore (_)

Pattern p = Pattern.compile("[^a-z0-9_.]", Pattern.CASE_INSENSITIVE);
Matcher m = p.matcher(i.getFileName());

boolean specialCharFound = m.find(); //this will return true if any other characters are found

^ means not a-z, letters and I added _ and ., but it doesn't work. Any idea how to add '_' '.' '-' characters?

Answer 1

Use Pattern.compile("[\w\s.-]+") and m.matches():

Pattern p = Pattern.compile("[\w\s.-]+");
Matcher m = p.matcher(i.getFileName());
boolean isValid = m.matches();

See regex proof.

Explanation

[ws.-]+                any character of: word characters (a-z, A-
                           Z, 0-9, _), whitespace (
, 
, , f,
                           and " "), '.', '-' (1 or more times
                           (matching the most amount possible))