com.google.cloud.dataflow.sdk.coders.MapCoder.java Source code

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Here is the source code for com.google.cloud.dataflow.sdk.coders.MapCoder.java

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/*
 * Copyright (C) 2015 Google Inc.
 *
 * 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.cloud.dataflow.sdk.coders;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.cloud.dataflow.sdk.util.PropertyNames;
import com.google.cloud.dataflow.sdk.util.common.ElementByteSizeObserver;
import com.google.common.collect.Maps;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

/**
 * A {@link Coder} for {@link Map Maps} that encodes them according to provided
 * coders for keys and values.
 *
 * @param <K> the type of the keys of the KVs being transcoded
 * @param <V> the type of the values of the KVs being transcoded
 */
public class MapCoder<K, V> extends MapCoderBase<Map<K, V>> {
    /**
     * Produces a MapCoder with the given keyCoder and valueCoder.
     */
    public static <K, V> MapCoder<K, V> of(Coder<K> keyCoder, Coder<V> valueCoder) {
        return new MapCoder<>(keyCoder, valueCoder);
    }

    @JsonCreator
    public static MapCoder<?, ?> of(@JsonProperty(PropertyNames.COMPONENT_ENCODINGS) List<Coder<?>> components) {
        checkArgument(components.size() == 2, "Expecting 2 components, got " + components.size());
        return of((Coder<?>) components.get(0), (Coder<?>) components.get(1));
    }

    /**
     * Returns the key and value for an arbitrary element of this map,
     * if it is non-empty, otherwise returns {@code null}.
     */
    public static <K, V> List<Object> getInstanceComponents(Map<K, V> exampleValue) {
        for (Map.Entry<K, V> entry : exampleValue.entrySet()) {
            return Arrays.asList(entry.getKey(), entry.getValue());
        }
        return null;
    }

    public Coder<K> getKeyCoder() {
        return keyCoder;
    }

    public Coder<V> getValueCoder() {
        return valueCoder;
    }

    /////////////////////////////////////////////////////////////////////////////

    Coder<K> keyCoder;
    Coder<V> valueCoder;

    MapCoder(Coder<K> keyCoder, Coder<V> valueCoder) {
        this.keyCoder = keyCoder;
        this.valueCoder = valueCoder;
    }

    @Override
    public void encode(Map<K, V> map, OutputStream outStream, Context context) throws IOException, CoderException {
        if (map == null) {
            throw new CoderException("cannot encode a null Map");
        }
        DataOutputStream dataOutStream = new DataOutputStream(outStream);
        dataOutStream.writeInt(map.size());
        for (Entry<K, V> entry : map.entrySet()) {
            keyCoder.encode(entry.getKey(), outStream, context.nested());
            valueCoder.encode(entry.getValue(), outStream, context.nested());
        }
        dataOutStream.flush();
    }

    @Override
    public Map<K, V> decode(InputStream inStream, Context context) throws IOException, CoderException {
        DataInputStream dataInStream = new DataInputStream(inStream);
        int size = dataInStream.readInt();
        Map<K, V> retval = Maps.newHashMapWithExpectedSize(size);
        for (int i = 0; i < size; ++i) {
            K key = keyCoder.decode(inStream, context.nested());
            V value = valueCoder.decode(inStream, context.nested());
            retval.put(key, value);
        }
        return retval;
    }

    /**
     * {@inheritDoc}
     *
     * @return a {@link List} containing the key coder at index 0 at the and value coder at index 1.
     */
    @Override
    public List<? extends Coder<?>> getCoderArguments() {
        return Arrays.asList(keyCoder, valueCoder);
    }

    /**
     * {@inheritDoc}
     *
     * @throws NonDeterministicException always. Not all maps have a deterministic encoding.
     * For example, {@code HashMap} comparison does not depend on element order, so
     * two {@code HashMap} instances may be equal but produce different encodings.
     */
    @Override
    public void verifyDeterministic() throws NonDeterministicException {
        throw new NonDeterministicException(this, "Ordering of entries in a Map may be non-deterministic.");
    }

    @Override
    public void registerByteSizeObserver(Map<K, V> map, ElementByteSizeObserver observer, Context context)
            throws Exception {
        observer.update(4L);
        for (Entry<K, V> entry : map.entrySet()) {
            keyCoder.registerByteSizeObserver(entry.getKey(), observer, context.nested());
            valueCoder.registerByteSizeObserver(entry.getValue(), observer, context.nested());
        }
    }
}