1 /*
2 * Copyright 2017 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License,
5 * version 2.0 (the "License"); you may not use this file except in compliance
6 * with the License. You may obtain a copy of the License at:
7 *
8 * https://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13 * License for the specific language governing permissions and limitations
14 * under the License.
15 */
16 package io.netty.resolver.dns;
17
18 import java.util.List;
19
20 /**
21 * A {@link DnsServerAddressStreamProvider} which iterates through a collection of
22 * {@link DnsServerAddressStreamProvider} until the first non-{@code null} result is found.
23 */
24 public final class MultiDnsServerAddressStreamProvider implements DnsServerAddressStreamProvider {
25 private final DnsServerAddressStreamProvider[] providers;
26
27 /**
28 * Create a new instance.
29 * @param providers The providers to use for DNS resolution. They will be queried in order.
30 */
31 public MultiDnsServerAddressStreamProvider(List<DnsServerAddressStreamProvider> providers) {
32 this.providers = providers.toArray(new DnsServerAddressStreamProvider[0]);
33 }
34
35 /**
36 * Create a new instance.
37 * @param providers The providers to use for DNS resolution. They will be queried in order.
38 */
39 public MultiDnsServerAddressStreamProvider(DnsServerAddressStreamProvider... providers) {
40 this.providers = providers.clone();
41 }
42
43 @Override
44 public DnsServerAddressStream nameServerAddressStream(String hostname) {
45 for (DnsServerAddressStreamProvider provider : providers) {
46 DnsServerAddressStream stream = provider.nameServerAddressStream(hostname);
47 if (stream != null) {
48 return stream;
49 }
50 }
51 return null;
52 }
53 }