guava/src/com/google/common/util/concurrent/ForwardingCheckedFuture.java

/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed 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
 *
 * http://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 com.google.common.util.concurrent;

import com.google.common.annotations.Beta;
import com.google.common.base.Preconditions;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * A future which forwards all its method calls to another future. Subclasses
 * should override one or more methods to modify the behavior of the backing 
 * future as desired per the <a href=
 * "http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p>Most subclasses can simply extend {@link SimpleForwardingCheckedFuture}.
 * 
 * @param <V> The result type returned by this Future's {@code get} method
 * @param <X> The type of the Exception thrown by the Future's 
 *            {@code checkedGet} method
 *
 * @author Anthony Zana
 * @since 9.0
 */
@Beta
public abstract class ForwardingCheckedFuture<V, X extends Exception> 
    extends ForwardingListenableFuture<V> implements CheckedFuture<V, X> {

  @Override
  public V checkedGet() throws X {
    return delegate().checkedGet();
  }

  @Override
  public V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, X {
    return delegate().checkedGet(timeout, unit);
  }

  @Override
  protected abstract CheckedFuture<V, X> delegate();

  // TODO(cpovirk): Use Standard Javadoc form for SimpleForwarding*
  /**
   * A simplified version of {@link ForwardingCheckedFuture} where subclasses
   * can pass in an already constructed {@link CheckedFuture} as the delegate.
   * 
   * @since 9.0
   */
  @Beta
  public abstract static class SimpleForwardingCheckedFuture<
      V, X extends Exception> extends ForwardingCheckedFuture<V, X> {
    private final CheckedFuture<V, X> delegate;

    protected SimpleForwardingCheckedFuture(CheckedFuture<V, X> delegate) {
      this.delegate = Preconditions.checkNotNull(delegate);
    }

    @Override
    protected final CheckedFuture<V, X> delegate() {
      return delegate;
    }
  }
}