flink-core/src/main/java/org/apache/flink/api/common/typeutils/base/AbstractMapSerializer.java

/*
 * 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.flink.api.common.typeutils.base;

import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataOutputView;
import org.apache.flink.util.Preconditions;

import java.io.IOException;
import java.util.Map;

/**
 * Base serializer for {@link Map}. The serializer relies on a key serializer
 * and a value serializer for the serialization of the map's key-value pairs.
 *
 * <p>The serialization format for the map is as follows: four bytes for the
 * length of the map, followed by the serialized representation of each
 * key-value pair. To allow null values, each value is prefixed by a null flag.
 *
 * @param <K> The type of the keys in the map.
 * @param <V> The type of the values in the map.
 * @param <M> The type of the map.
 */
abstract class AbstractMapSerializer<K, V, M extends Map<K, V>> extends TypeSerializer<M> {

	private static final long serialVersionUID = 1L;

	/** The serializer for the keys in the map */
	final TypeSerializer<K> keySerializer;

	/** The serializer for the values in the map */
	final TypeSerializer<V> valueSerializer;

	/**
	 * Creates a map serializer that uses the given serializers to serialize the key-value pairs in the map.
	 *
	 * @param keySerializer The serializer for the keys in the map
	 * @param valueSerializer The serializer for the values in the map
	 */
	AbstractMapSerializer(
		TypeSerializer<K> keySerializer,
		TypeSerializer<V> valueSerializer
	) {
		Preconditions.checkNotNull(keySerializer,
			"The key serializer must not be null");
		Preconditions.checkNotNull(valueSerializer,
			"The value serializer must not be null.");
		this.keySerializer = keySerializer;
		this.valueSerializer = valueSerializer;
	}

	// ------------------------------------------------------------------------

	/**
	 * Returns the serializer for the keys in the map.
	 *
	 * @return The serializer for the keys in the map.
	 */
	public TypeSerializer<K> getKeySerializer() {
		return keySerializer;
	}

	/**
	 * Returns the serializer for the values in the map.
	 *
	 * @return The serializer for the values in the map.
	 */
	public TypeSerializer<V> getValueSerializer() {
		return valueSerializer;
	}

	// ------------------------------------------------------------------------
	//  Type Serializer implementation
	// ------------------------------------------------------------------------

	@Override
	public boolean isImmutableType() {
		return false;
	}

	@Override
	public M copy(M from) {
		M newMap = createInstance();

		for (Map.Entry<K, V> entry : from.entrySet()) {
			K newKey = entry.getKey() == null ? null : keySerializer.copy(entry.getKey());
			V newValue = entry.getValue() == null ? null : valueSerializer.copy(entry.getValue());

			newMap.put(newKey, newValue);
		}

		return newMap;
	}

	@Override
	public M copy(M from, M reuse) {
		return copy(from);
	}

	@Override
	public int getLength() {
		return -1; // var length
	}

	@Override
	public void serialize(M map, DataOutputView target) throws IOException {
		final int size = map.size();
		target.writeInt(size);

		for (Map.Entry<K, V> entry : map.entrySet()) {
			keySerializer.serialize(entry.getKey(), target);

			if (entry.getValue() == null) {
				target.writeBoolean(true);
			} else {
				target.writeBoolean(false);
				valueSerializer.serialize(entry.getValue(), target);
			}
		}
	}

	@Override
	public M deserialize(DataInputView source) throws IOException {
		final int size = source.readInt();

		final M map = createInstance();
		for (int i = 0; i < size; ++i) {
			K key = keySerializer.deserialize(source);

			boolean isNull = source.readBoolean();
			V value = isNull ? null : valueSerializer.deserialize(source);

			map.put(key, value);
		}

		return map;
	}

	@Override
	public M deserialize(M reuse, DataInputView source) throws IOException {
		return deserialize(source);
	}

	@Override
	public void copy(DataInputView source, DataOutputView target) throws IOException {
		final int size = source.readInt();
		target.writeInt(size);

		for (int i = 0; i < size; ++i) {
			keySerializer.copy(source, target);

			boolean isNull = source.readBoolean();
			target.writeBoolean(isNull);

			if (!isNull) {
				valueSerializer.copy(source, target);
			}
		}
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}

		if (o == null || getClass() != o.getClass()) {
			return false;
		}

		AbstractMapSerializer<?, ?, ?> that = (AbstractMapSerializer<?, ?, ?>) o;

		return keySerializer.equals(that.keySerializer) &&
			valueSerializer.equals(that.valueSerializer);
	}

	@Override
	public int hashCode() {
		int result = keySerializer.hashCode();
		result = 31 * result + valueSerializer.hashCode();
		return result;
	}
}