JAVA EE: How to write a regex to validate the username | Java Regex

Thursday 21 December 2017

How to write a regex to validate the username | Java Regex | Regex in java

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How to write a regex to validate the username | Java Regex | Regex in java

UserNameValidator.java

import java.util.regex.Matcher;

import java.util.regex.Pattern;

/**

 * 

 * How to validate username with regular expression

 *

 */

public class UserNameValidator

{

    private Pattern pattern;

    private Matcher matcher;

    private static final String USERNAME_REGEX = "^[a-z0-9_-]{3,15}$";

    public UserNameValidator()

    {

        pattern = Pattern.compile(USERNAME_REGEX);

    }

    /*

     * Validate username with regular expression

     * 

     * @param username username for validation

     * 

     * @return true valid username, false invalid username

     */

    public boolean validate(final String username)

    {

        matcher = pattern.matcher(username);

        return matcher.matches();

    }

}

RegexDemo.java

/**

 *

 * How to validate username with regular expression

 *

 */

public class RegexDemo

{

    public static void main(String[] args)

    {

        UserNameValidator unValidator = new UserNameValidator();

        System.out.println("'peter34' is valid userName? = "+unValidator.validate("peter34"));

        System.out.println("'peter_34' is valid userName? = "+unValidator.validate("peter_34"));

        System.out.println("'peter-34' is valid userName? = "+unValidator.validate("peter-34"));

        System.out.println();

        /*

         * too short, min 3 characters

         */

        System.out.println("'pk' is valid userName? = "+unValidator.validate("pk"));

        /*

         * “@" character is not allow

         */

        System.out.println("'peter@89' is valid userName? = "+unValidator.validate("peter@89"));

        /*

         * too long, max characters of 15

         */

        System.out.println("'peter11111323445' is valid userName? = "+unValidator.validate("peter11111323445"));

    }

}

Output

'peter34' is valid userName? = true

'peter_34' is valid userName? = true

'peter-34' is valid userName? = true

'pk' is valid userName? = false

'peter@89' is valid userName? = false

'peter11111323445' is valid userName? = false