EmailValidator.java

package cc.blynk.utils.validators;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * <p>Perform email validations.</p>
 * <p>
 * Based on a script by <a href="mailto:stamhankar@hotmail.com">Sandeep V. Tamhankar</a>
 * http://javascript.internet.com
 * </p>
 * <p>
 * This implementation is not guaranteed to catch all possible errors in an email address.
 * </p>.
 *
 * @version $Revision: 1723573 $
 * @since Validator 1.4
 */
public class EmailValidator {

    private static final String SPECIAL_CHARS = "\\p{Cntrl}\\(\\)<>@,;:'\\\\\\\"\\.\\[\\]";
    private static final String VALID_CHARS = "(\\\\.)|[^\\s" + SPECIAL_CHARS + "]";
    private static final String QUOTED_USER = "(\"(\\\\\"|[^\"])*\")";
    private static final String WORD = "((" + VALID_CHARS + "|')+|" + QUOTED_USER + ")";

    private static final String EMAIL_REGEX = "^\\s*?(.+)@(.+?)\\s*$";
    private static final String IP_DOMAIN_REGEX = "^\\[(.*)\\]$";
    private static final String USER_REGEX = "^\\s*" + WORD + "(\\." + WORD + ")*$";

    private static final Pattern EMAIL_PATTERN = Pattern.compile(EMAIL_REGEX);
    private static final Pattern IP_DOMAIN_PATTERN = Pattern.compile(IP_DOMAIN_REGEX);
    private static final Pattern USER_PATTERN = Pattern.compile(USER_REGEX);

    private static final int MAX_USERNAME_LEN = 64;

    private final boolean allowLocal;
    private final boolean allowTld;

    /**
     * Singleton instance of this class, which
     *  doesn't consider local addresses as valid.
     */
    private static final EmailValidator EMAIL_VALIDATOR = new EmailValidator(false, false);


    /**
     * Returns the Singleton instance of this validator.
     *
     * @return singleton instance of this validator.
     */
    public static EmailValidator getInstance() {
        return EMAIL_VALIDATOR;
    }

    /**
     * Protected constructor for subclasses to use.
     *
     * @param allowLocal Should local addresses be considered valid?
     * @param allowTld Should TLDs be allowed?
     */
    protected EmailValidator(boolean allowLocal, boolean allowTld) {
        super();
        this.allowLocal = allowLocal;
        this.allowTld = allowTld;
    }

    /**
     * <p>Checks if a field has a valid e-mail address.</p>
     *
     * @param email The value validation is being performed on.  A <code>null</code>
     *              value is considered invalid.
     * @return true if the email address is valid.
     */
    public boolean isValid(String email) {
        if (email.endsWith(".")) { // check this first - it's cheap!
            return false;
        }

        // Check the whole email address structure
        Matcher emailMatcher = EMAIL_PATTERN.matcher(email);
        if (!emailMatcher.matches()) {
            return false;
        }

        if (!isValidUser(emailMatcher.group(1))) {
            return false;
        }

        return isValidDomain(emailMatcher.group(2));

    }

    /**
     * Returns true if the domain component of an email address is valid.
     *
     * @param domain being validated, may be in IDN format
     * @return true if the email address's domain is valid.
     */
    protected boolean isValidDomain(String domain) {
        // see if domain is an IP address in brackets
        Matcher ipDomainMatcher = IP_DOMAIN_PATTERN.matcher(domain);

        if (ipDomainMatcher.matches()) {
            InetAddressValidator inetAddressValidator =
                    InetAddressValidator.getInstance();
            return inetAddressValidator.isValid(ipDomainMatcher.group(1));
        }
        // Domain is symbolic name
        DomainValidator domainValidator =
                DomainValidator.getInstance(allowLocal);
        if (allowTld) {
            return domainValidator.isValid(domain) || (!domain.startsWith(".") && domainValidator.isValidTld(domain));
        } else {
            return domainValidator.isValid(domain);
        }
    }

    /**
     * Returns true if the user component of an email address is valid.
     *
     * @param user being validated
     * @return true if the user name is valid.
     */
    protected boolean isValidUser(String user) {
        return !(user == null || user.length() > MAX_USERNAME_LEN) && USER_PATTERN.matcher(user).matches();
    }

}