org.apache.beam.sdk.coders.MapCoder.java Source code

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Here is the source code for org.apache.beam.sdk.coders.MapCoder.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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
 *
 *     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 org.apache.beam.sdk.coders;

import com.google.common.collect.Maps;
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.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import org.apache.beam.sdk.util.common.ElementByteSizeObserver;
import org.apache.beam.sdk.values.TypeDescriptor;
import org.apache.beam.sdk.values.TypeParameter;

/**
 * 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 StructuredCoder<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);
    }

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

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

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

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

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

    @Override
    public void encode(Map<K, V> map, OutputStream outStream) throws IOException, CoderException {
        encode(map, outStream, Context.NESTED);
    }

    @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);

        int size = map.size();
        dataOutStream.writeInt(size);
        if (size == 0) {
            return;
        }

        // Since we handled size == 0 above, entry is guaranteed to exist before and after loop
        Iterator<Entry<K, V>> iterator = map.entrySet().iterator();
        Entry<K, V> entry = iterator.next();
        while (iterator.hasNext()) {
            keyCoder.encode(entry.getKey(), outStream);
            valueCoder.encode(entry.getValue(), outStream);
            entry = iterator.next();
        }

        keyCoder.encode(entry.getKey(), outStream);
        valueCoder.encode(entry.getValue(), outStream, context);
        // no flush needed as DataOutputStream does not buffer
    }

    @Override
    public Map<K, V> decode(InputStream inStream) throws IOException, CoderException {
        return decode(inStream, Context.NESTED);
    }

    @Override
    public Map<K, V> decode(InputStream inStream, Context context) throws IOException, CoderException {
        DataInputStream dataInStream = new DataInputStream(inStream);
        int size = dataInStream.readInt();
        if (size == 0) {
            return Collections.emptyMap();
        }

        Map<K, V> retval = Maps.newHashMapWithExpectedSize(size);
        for (int i = 0; i < size - 1; ++i) {
            K key = keyCoder.decode(inStream);
            V value = valueCoder.decode(inStream);
            retval.put(key, value);
        }

        K key = keyCoder.decode(inStream);
        V value = valueCoder.decode(inStream, context);
        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) throws Exception {
        observer.update(4L);
        if (map.isEmpty()) {
            return;
        }
        Iterator<Entry<K, V>> entries = map.entrySet().iterator();
        Entry<K, V> entry = entries.next();
        while (entries.hasNext()) {
            keyCoder.registerByteSizeObserver(entry.getKey(), observer);
            valueCoder.registerByteSizeObserver(entry.getValue(), observer);
            entry = entries.next();
        }
        keyCoder.registerByteSizeObserver(entry.getKey(), observer);
        valueCoder.registerByteSizeObserver(entry.getValue(), observer);
    }

    @Override
    public TypeDescriptor<Map<K, V>> getEncodedTypeDescriptor() {
        return new TypeDescriptor<Map<K, V>>() {
        }.where(new TypeParameter<K>() {
        }, keyCoder.getEncodedTypeDescriptor()).where(new TypeParameter<V>() {
        }, valueCoder.getEncodedTypeDescriptor());
    }
}