/*
* 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.
*
* <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 {@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 {@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 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}
/**代码未完, 请加载全部代码(NowJava.com).**/