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   /*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  
  package io.netty.resolver;
  
  import io.netty.util.concurrent.EventExecutor;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.Promise;
  
  import java.util.List;
  
  import static io.netty.util.internal.ObjectUtil.*;
  
  /**
   * A skeletal {@link NameResolver} implementation.
   */
  public abstract class SimpleNameResolver<T> implements NameResolver<T> {
  
      private final EventExecutor executor;
  
      /**
       * @param executor the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned
       *                 by {@link #resolve(String)}
       */
      protected SimpleNameResolver(EventExecutor executor) {
          this.executor = checkNotNull(executor, "executor");
      }
  
      /**
       * Returns the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned
       * by {@link #resolve(String)}.
       */
      protected EventExecutor executor() {
          return executor;
      }
  
      @Override
      public final Future<T> resolve(String inetHost) {
          final Promise<T> promise = executor().newPromise();
          return resolve(inetHost, promise);
      }
  
      @Override
      public Future<T> resolve(String inetHost, Promise<T> promise) {
          checkNotNull(promise, "promise");
  
          try {
              doResolve(inetHost, promise);
              return promise;
          } catch (Exception e) {
              return promise.setFailure(e);
          }
      }
  
      @Override
      public final Future<List<T>> resolveAll(String inetHost) {
          final Promise<List<T>> promise = executor().newPromise();
          return resolveAll(inetHost, promise);
      }
  
      @Override
      public Future<List<T>> resolveAll(String inetHost, Promise<List<T>> promise) {
          checkNotNull(promise, "promise");
  
          try {
              doResolveAll(inetHost, promise);
              return promise;
          } catch (Exception e) {
              return promise.setFailure(e);
          }
      }
  
      /**
       * Invoked by {@link #resolve(String)} to perform the actual name resolution.
       */
      protected abstract void doResolve(String inetHost, Promise<T> promise) throws Exception;
  
      /**
       * Invoked by {@link #resolveAll(String)} to perform the actual name resolution.
       */
      protected abstract void doResolveAll(String inetHost, Promise<List<T>> promise) throws Exception;
  
      @Override
      public void close() { }
  }