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   /*
    * Copyright 2015 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 io.netty.util.internal.TypeParameterMatcher;
  
  import java.net.SocketAddress;
  import java.nio.channels.UnsupportedAddressTypeException;
  import java.util.Collections;
  import java.util.List;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * A skeletal {@link AddressResolver} implementation.
   */
  public abstract class AbstractAddressResolver<T extends SocketAddress> implements AddressResolver<T> {
  
      private final EventExecutor executor;
      private final TypeParameterMatcher matcher;
  
      /**
       * @param executor the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned
       *                 by {@link #resolve(SocketAddress)}
       */
      protected AbstractAddressResolver(EventExecutor executor) {
          this.executor = checkNotNull(executor, "executor");
          this.matcher = TypeParameterMatcher.find(this, AbstractAddressResolver.class, "T");
      }
  
      /**
       * @param executor the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned
       *                 by {@link #resolve(SocketAddress)}
       * @param addressType the type of the {@link SocketAddress} supported by this resolver
       */
      protected AbstractAddressResolver(EventExecutor executor, Class<? extends T> addressType) {
          this.executor = checkNotNull(executor, "executor");
          this.matcher = TypeParameterMatcher.get(addressType);
      }
  
      /**
       * Returns the {@link EventExecutor} which is used to notify the listeners of the {@link Future} returned
       * by {@link #resolve(SocketAddress)}.
       */
      protected EventExecutor executor() {
          return executor;
      }
  
      @Override
      public boolean isSupported(SocketAddress address) {
          return matcher.match(address);
      }
  
      @Override
      public final boolean isResolved(SocketAddress address) {
          if (!isSupported(address)) {
              throw new UnsupportedAddressTypeException();
          }
  
          @SuppressWarnings("unchecked")
          final T castAddress = (T) address;
          return doIsResolved(castAddress);
      }
  
      /**
       * Invoked by {@link #isResolved(SocketAddress)} to check if the specified {@code address} has been resolved
       * already.
       */
      protected abstract boolean doIsResolved(T address);
  
      @Override
      public final Future<T> resolve(SocketAddress address) {
          if (!isSupported(checkNotNull(address, "address"))) {
              // Address type not supported by the resolver
              return executor().newFailedFuture(new UnsupportedAddressTypeException());
          }
  
          if (isResolved(address)) {
              // Resolved already; no need to perform a lookup
              @SuppressWarnings("unchecked")
              final T cast = (T) address;
              return executor.newSucceededFuture(cast);
         }
 
         try {
             @SuppressWarnings("unchecked")
             final T cast = (T) address;
             final Promise<T> promise = executor().newPromise();
             doResolve(cast, promise);
             return promise;
         } catch (Exception e) {
             return executor().newFailedFuture(e);
         }
     }
 
     @Override
     public final Future<T> resolve(SocketAddress address, Promise<T> promise) {
         checkNotNull(address, "address");
         checkNotNull(promise, "promise");
 
         if (!isSupported(address)) {
             // Address type not supported by the resolver
             return promise.setFailure(new UnsupportedAddressTypeException());
         }
 
         if (isResolved(address)) {
             // Resolved already; no need to perform a lookup
             @SuppressWarnings("unchecked")
             final T cast = (T) address;
             return promise.setSuccess(cast);
         }
 
         try {
             @SuppressWarnings("unchecked")
             final T cast = (T) address;
             doResolve(cast, promise);
             return promise;
         } catch (Exception e) {
             return promise.setFailure(e);
         }
     }
 
     @Override
     public final Future<List<T>> resolveAll(SocketAddress address) {
         if (!isSupported(checkNotNull(address, "address"))) {
             // Address type not supported by the resolver
             return executor().newFailedFuture(new UnsupportedAddressTypeException());
         }
 
         if (isResolved(address)) {
             // Resolved already; no need to perform a lookup
             @SuppressWarnings("unchecked")
             final T cast = (T) address;
             return executor.newSucceededFuture(Collections.singletonList(cast));
         }
 
         try {
             @SuppressWarnings("unchecked")
             final T cast = (T) address;
             final Promise<List<T>> promise = executor().newPromise();
             doResolveAll(cast, promise);
             return promise;
         } catch (Exception e) {
             return executor().newFailedFuture(e);
         }
     }
 
     @Override
     public final Future<List<T>> resolveAll(SocketAddress address, Promise<List<T>> promise) {
         checkNotNull(address, "address");
         checkNotNull(promise, "promise");
 
         if (!isSupported(address)) {
             // Address type not supported by the resolver
             return promise.setFailure(new UnsupportedAddressTypeException());
         }
 
         if (isResolved(address)) {
             // Resolved already; no need to perform a lookup
             @SuppressWarnings("unchecked")
             final T cast = (T) address;
             return promise.setSuccess(Collections.singletonList(cast));
         }
 
         try {
             @SuppressWarnings("unchecked")
             final T cast = (T) address;
             doResolveAll(cast, promise);
             return promise;
         } catch (Exception e) {
             return promise.setFailure(e);
         }
     }
 
     /**
      * Invoked by {@link #resolve(SocketAddress)} to perform the actual name
      * resolution.
      */
     protected abstract void doResolve(T unresolvedAddress, Promise<T> promise) throws Exception;
 
     /**
      * Invoked by {@link #resolveAll(SocketAddress)} to perform the actual name
      * resolution.
      */
     protected abstract void doResolveAll(T unresolvedAddress, Promise<List<T>> promise) throws Exception;
 
     @Override
     public void close() { }
 }