    001    /*
    002     * Copyright (C) 2011 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.util.concurrent;
    018
    019    import com.google.common.annotations.Beta;
    020    import com.google.common.base.Preconditions;
    021
    022    import java.util.concurrent.TimeUnit;
    023    import java.util.concurrent.TimeoutException;
    024
    025    /**
    026     * A future which forwards all its method calls to another future. Subclasses
    027     * should override one or more methods to modify the behavior of the backing
    028     * future as desired per the <a href=
    029     * "http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
    030     *
    031     * <p>Most subclasses can simply extend {@link SimpleForwardingCheckedFuture}.
    032     *
    033     * @param <V> The result type returned by this Future's {@code get} method
    034     * @param <X> The type of the Exception thrown by the Future's
    035     *            {@code checkedGet} method
    036     *
    037     * @author Anthony Zana
    038     * @since 9.0
    039     */
    040    @Beta
    041    public abstract class ForwardingCheckedFuture<V, X extends Exception>
    042        extends ForwardingListenableFuture<V> implements CheckedFuture<V, X> {
    043
    044      @Override
    045      public V checkedGet() throws X {
    046        return delegate().checkedGet();
    047      }
    048
    049      @Override
    050      public V checkedGet(long timeout, TimeUnit unit) throws TimeoutException, X {
    051        return delegate().checkedGet(timeout, unit);
    052      }
    053
    054      @Override
    055      protected abstract CheckedFuture<V, X> delegate();
    056
    057      // TODO(cpovirk): Use Standard Javadoc form for SimpleForwarding*
    058      /**
    059       * A simplified version of {@link ForwardingCheckedFuture} where subclasses
    060       * can pass in an already constructed {@link CheckedFuture} as the delegate.
    061       *
    062       * @since 9.0
    063       */
    064      @Beta
    065      public abstract static class SimpleForwardingCheckedFuture<
    066          V, X extends Exception> extends ForwardingCheckedFuture<V, X> {
    067        private final CheckedFuture<V, X> delegate;
    068
    069        protected SimpleForwardingCheckedFuture(CheckedFuture<V, X> delegate) {
    070          this.delegate = Preconditions.checkNotNull(delegate);
    071        }
    072
    073        @Override
    074        protected final CheckedFuture<V, X> delegate() {
    075          return delegate;
    076        }
    077      }
    078    }