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1   /*
2    * Copyright 2014 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  
17  package io.netty.resolver;
18  
19  import io.netty.util.concurrent.EventExecutor;
20  import io.netty.util.concurrent.Future;
21  import io.netty.util.concurrent.Promise;
22  
23  import java.util.List;
24  
25  import static io.netty.util.internal.ObjectUtil.*;
26  
27  /**
28   * A skeletal {@link NameResolver} implementation.
29   */
30  public abstract class SimpleNameResolver<T> implements NameResolver<T> {
31  
32      private final EventExecutor executor;
33  
34      /**
35       * @param executor the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned
36       *                 by {@link #resolve(String)}
37       */
38      protected SimpleNameResolver(EventExecutor executor) {
39          this.executor = checkNotNull(executor, "executor");
40      }
41  
42      /**
43       * Returns the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned
44       * by {@link #resolve(String)}.
45       */
46      protected EventExecutor executor() {
47          return executor;
48      }
49  
50      @Override
51      public final Future<T> resolve(String inetHost) {
52          final Promise<T> promise = executor().newPromise();
53          return resolve(inetHost, promise);
54      }
55  
56      @Override
57      public Future<T> resolve(String inetHost, Promise<T> promise) {
58          checkNotNull(promise, "promise");
59  
60          try {
61              doResolve(inetHost, promise);
62              return promise;
63          } catch (Exception e) {
64              return promise.setFailure(e);
65          }
66      }
67  
68      @Override
69      public final Future<List<T>> resolveAll(String inetHost) {
70          final Promise<List<T>> promise = executor().newPromise();
71          return resolveAll(inetHost, promise);
72      }
73  
74      @Override
75      public Future<List<T>> resolveAll(String inetHost, Promise<List<T>> promise) {
76          checkNotNull(promise, "promise");
77  
78          try {
79              doResolveAll(inetHost, promise);
80              return promise;
81          } catch (Exception e) {
82              return promise.setFailure(e);
83          }
84      }
85  
86      /**
87       * Invoked by {@link #resolve(String)} to perform the actual name resolution.
88       */
89      protected abstract void doResolve(String inetHost, Promise<T> promise) throws Exception;
90  
91      /**
92       * Invoked by {@link #resolveAll(String)} to perform the actual name resolution.
93       */
94      protected abstract void doResolveAll(String inetHost, Promise<List<T>> promise) throws Exception;
95  
96      @Override
97      public void close() { }
98  }