https://openjdk.java.net/ 
/*
 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.naming.ldap.spi;

import javax.naming.Context;
import javax.naming.NamingException;
import java.util.Map;
import java.util.Optional;


Service-provider class for DNS lookups when performing LDAP operations.

 An LDAP DNS provider is a concrete subclass of this class that has a zero-argument constructor. LDAP DNS providers are located using the ServiceLoader facility, as specified by InitialDirectContext. The ServiceLoader is used to create and register implementations of LdapDnsProvider. 
 An LDAP DNS provider can be used in environments where the default DNS resolution mechanism is not sufficient to accurately pinpoint the correct LDAP servers needed to perform LDAP operations. For example, in an environment containing a mix of ldap and ldaps servers you may want the LdapContext to query ldaps servers only. 
Since:12
/**
 * Service-provider class for DNS lookups when performing LDAP operations.
 *
 * <p> An LDAP DNS provider is a concrete subclass of this class that
 * has a zero-argument constructor. LDAP DNS providers are located using the
 * ServiceLoader facility, as specified by
 * {@linkplain javax.naming.directory.InitialDirContext InitialDirectContext}.
 *
 * The
 * {@link java.util.ServiceLoader ServiceLoader} is used to create and register
 * implementations of {@code LdapDnsProvider}.
 *
 * <p> An LDAP DNS provider can be used in environments where the default
 * DNS resolution mechanism is not sufficient to accurately pinpoint the
 * correct LDAP servers needed to perform LDAP operations. For example, in an
 * environment containing a mix of {@code ldap} and {@code ldaps} servers
 * you may want the {@linkplain javax.naming.ldap.LdapContext LdapContext}
 * to query {@code ldaps} servers only.
 *
 * @since 12
 */
public abstract class LdapDnsProvider {

    // The {@code RuntimePermission("ldapDnsProvider")} is
    // necessary to subclass and instantiate the {@code LdapDnsProvider} class.
    private static final RuntimePermission DNSPROVIDER_PERMISSION =
            new RuntimePermission("ldapDnsProvider");

    
Creates a new instance of LdapDnsProvider. 
Throws:
  • SecurityException – if a security manager is present and its checkPermission method doesn't allow the RuntimePermission("ldapDnsProvider").
/**
     * Creates a new instance of {@code LdapDnsProvider}.
     *
     * @throws SecurityException if a security manager is present and its
     *                           {@code checkPermission} method doesn't allow
     *                           the {@code RuntimePermission("ldapDnsProvider")}.
     */
    protected LdapDnsProvider() {
        this(checkPermission());
    }

    private LdapDnsProvider(Void unused) {
        // nothing to do.
    }

    private static Void checkPermission() {
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(DNSPROVIDER_PERMISSION);
        }
        return null;
    }

    
Lookup the endpoints and domain name for the given Context provider URL and environment. The resolved endpoints and domain name are returned as an LdapDnsProviderResult. 
 An endpoint is a String representation of an LDAP URL which points to an LDAP server to be used for LDAP operations. The syntax of an LDAP URL is defined by 
RFC 2255: The LDAP URL Format.

Params:
Throws:
Returns: an LdapDnsProviderResult or empty Optional if the lookup fails.
/**
     * Lookup the endpoints and domain name for the given {@link Context}
     * {@link Context#PROVIDER_URL provider URL} and environment. The resolved
     * endpoints and domain name are returned as an
     * {@link LdapDnsProviderResult}.
     *
     * <p> An endpoint is a {@code String} representation of an LDAP URL which
     * points to an LDAP server to be used for LDAP operations. The syntax of
     * an LDAP URL is defined by <a href="http://www.ietf.org/rfc/rfc2255.txt">
     * <i>RFC&nbsp;2255: The LDAP URL Format</i></a>.
     *
     * @param url   The {@link Context} {@link Context#PROVIDER_URL provider URL}
     * @param env   The {@link Context} environment.
     *
     * @return  an {@link LdapDnsProviderResult} or empty {@code Optional}
     *          if the lookup fails.
     *
     * @throws NamingException      if the {@code url} is not valid or an error
     *                              occurred while performing the lookup.
     * @throws NullPointerException if either {@code url} or {@code env} are
     *                              {@code null}.
     */
    public abstract Optional<LdapDnsProviderResult> lookupEndpoints(
            String url, Map<?,?> env) throws NamingException;

}