limiting characters after dot - java

Question

Hey so I'm doing a project for school. We have to code a virtual atm machine. You would have to log in with your student mail.

My question is : How do I limit character length after a dot(.)?

public boolean validUsername(String username) {
        Boolean oneAT = false;
        for (int i=0; i < username.length(); i++) {
            if (username.contains("@") && username.contains(".") &&{
                oneAT = true;
            }
        }

        return oneAT;
    }

The function checks if the username typed, contains a @ and a .(dot). Is there a way to limit character length to three after the dot ? Otherwise the user can write [email protected]

Answer 1

It's easier to validate the username with a regular expression

public boolean validUsername(String username) {
    Pattern pattern = Pattern.compile("^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$");
    Matcher matcher = pattern.matcher(username);
    return matcher.matches();
}

The expression validates if the username is a valid email address and returns true if so.

Answer 2

To answer the specific question, you can limit the size by checking the size of the substring after the dot (assuming you only have on dot in the string):

afterDot = username.substring(username.indexOf("."))

But as stated by ZouZou, you should properly validate your email address (there's several other things to check for). Take a look at the example here: http://examples.javacodegeeks.com/core-java/util/regex/matcher/validate-email-address-with-java-regular-expression-example/

Answer 3

This should be helpful:

if (username.contains("@") && username.contains(".") && ((username.length() - username.lastIndexOf(".") <= 3)) {

Essentially it checks whether the difference of the String length and the last occurrence of dot is smaller or equal than 3. This handles emails like [email protected] as well.