1 /*
2 * Copyright 2015 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;
17
18 import io.netty.util.concurrent.EventExecutor;
19 import io.netty.util.concurrent.Future;
20
21 import java.net.InetAddress;
22 import java.net.InetSocketAddress;
23
24 /**
25 * A skeletal {@link NameResolver} implementation that resolves {@link InetAddress}.
26 */
27 public abstract class InetNameResolver extends SimpleNameResolver<InetAddress> {
28 private volatile AddressResolver<InetSocketAddress> addressResolver;
29
30 /**
31 * @param executor the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned
32 * by {@link #resolve(String)}
33 */
34 protected InetNameResolver(EventExecutor executor) {
35 super(executor);
36 }
37
38 /**
39 * Return a {@link AddressResolver} that will use this name resolver underneath.
40 * It's cached internally, so the same instance is always returned.
41 */
42 public AddressResolver<InetSocketAddress> asAddressResolver() {
43 AddressResolver<InetSocketAddress> result = addressResolver;
44 if (result == null) {
45 synchronized (this) {
46 result = addressResolver;
47 if (result == null) {
48 addressResolver = result = new InetSocketAddressResolver(executor(), this);
49 }
50 }
51 }
52 return result;
53 }
54 }