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Microsoft JDBC Driver for SQL Server.

There is a newer version: 12.8.1.jre11

/*
 * Microsoft JDBC Driver for SQL Server Copyright(c) Microsoft Corporation All rights reserved. This program is made
 * available under the terms of the MIT License. See the LICENSE file in the project root for more information.
 */
package com.microsoft.sqlserver.jdbc.dns;

import java.util.Set;

import javax.naming.NameNotFoundException;
import javax.naming.NamingException;

/**
 * Represents a DNS Kerberos Locator
 */
public final class DNSKerberosLocator {

    private DNSKerberosLocator() {}

    /**
     * Returns whether a realm is valid by retrieving the KDC list in DNS SRV records.
     * This will only work if DNS lookup is setup properly or the realms are properly defined in krb5 config file.
     * Otherwise this will fail since the realm cannot be found.
     *
     * @param realmName
     *        the realm to test
     * @return true if realm is valid, false otherwise
     * @throws NamingException
     *         if DNS failed, so realm existence cannot be determined
     */
    public static boolean isRealmValid(String realmName) throws NamingException {
        if (realmName == null || realmName.length() < 2) {
            return false;
        }
        if (realmName.startsWith(".")) {
            realmName = realmName.substring(1);
        }
        try {
            Set records = DNSUtilities.findSrvRecords("_kerberos._udp." + realmName);
            return !records.isEmpty();
        } catch (NameNotFoundException wrongDomainException) {
            // config error - domain controller cannot be located via DNS 
            return false;
        }
    }
}