dagger.producers.internal.MapProducer.java Source code

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Here is the source code for dagger.producers.internal.MapProducer.java

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/*
 * Copyright (C) 2016 The Dagger 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 dagger.producers.internal;

import static com.google.common.util.concurrent.Futures.transform;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;

import com.google.common.base.Function;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;
import com.google.common.util.concurrent.AsyncFunction;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import dagger.producers.Producer;
import java.util.List;
import java.util.Map;

/**
 * A {@link Producer} implementation used to implement {@link Map} bindings. This producer returns a
 * {@code Map<K, V>} which is populated by calls to the delegate {@link Producer#get} methods.
 *
 * @author Jesse Beder
 */
public final class MapProducer<K, V> extends AbstractProducer<Map<K, V>> {
    private final Producer<Map<K, Producer<V>>> mapProducerProducer;

    private MapProducer(Producer<Map<K, Producer<V>>> mapProducerProducer) {
        this.mapProducerProducer = mapProducerProducer;
    }

    /**
     * Returns a producer of {@code Map<K, V>}, where the map is derived from the given map of
     * producers by waiting for those producers' resulting futures. The iteration order mirrors the
     * order of the input map.
     *
     * <p>If any of the delegate producers, or their resulting values, are null, then this producer's
     * future will fail with a {@link NullPointerException}.
     *
     * <p>Canceling this future will attempt to cancel all of the component futures, and if any of the
     * component futures fails or is canceled, this one is, too.
     */
    public static <K, V> MapProducer<K, V> create(Producer<Map<K, Producer<V>>> mapProducerProducer) {
        return new MapProducer<K, V>(mapProducerProducer);
    }

    @Override
    public ListenableFuture<Map<K, V>> compute() {
        return Futures.transformAsync(mapProducerProducer.get(),
                new AsyncFunction<Map<K, Producer<V>>, Map<K, V>>() {
                    @Override
                    public ListenableFuture<Map<K, V>> apply(final Map<K, Producer<V>> map) {
                        // TODO(beder): Use Futures.whenAllComplete when Guava 20 is released.
                        return transform(
                                Futures.allAsList(
                                        Iterables.transform(map.entrySet(), MapProducer.<K, V>entryUnwrapper())),
                                new Function<List<Map.Entry<K, V>>, Map<K, V>>() {
                                    @Override
                                    public Map<K, V> apply(List<Map.Entry<K, V>> entries) {
                                        return ImmutableMap.copyOf(entries);
                                    }
                                }, directExecutor());
                    }
                }, directExecutor());
    }

    private static final Function<Map.Entry<Object, Producer<Object>>, ListenableFuture<Map.Entry<Object, Object>>> ENTRY_UNWRAPPER = new Function<Map.Entry<Object, Producer<Object>>, ListenableFuture<Map.Entry<Object, Object>>>() {
        @Override
        public ListenableFuture<Map.Entry<Object, Object>> apply(final Map.Entry<Object, Producer<Object>> entry) {
            return transform(entry.getValue().get(), new Function<Object, Map.Entry<Object, Object>>() {
                @Override
                public Map.Entry<Object, Object> apply(Object value) {
                    return Maps.immutableEntry(entry.getKey(), value);
                }
            }, directExecutor());
        }
    };

    @SuppressWarnings({ "unchecked", "rawtypes" }) // bivariate implementation
    private static <K, V> Function<Map.Entry<K, Producer<V>>, ListenableFuture<Map.Entry<K, V>>> entryUnwrapper() {
        return (Function) ENTRY_UNWRAPPER;
    }
}