Username Validation Java -

i'm new in java, don't know language. have simple html form fill register login.

my problem detail in username, can't have invalid character (accents , symbols, example) , don´t know how check username characters.

i used request.getparameter("username") username in string variable.

string username = request.getparameter("username");

how can proceed?

boolean matches(string regex)
tells whether or not string matches given regular expression.

string username = request.getparameter("username"); boolean valid = (username != null) && username.matches("[a-za-z0-9_]+");

but if used multiple times more efficient use pattern:

pattern pattern = pattern.compile("[a-za-z0-9_]+");

and use each time:

boolean valid = (username != null) && pattern.matcher(username).matches();

Dil