/*
 * 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;

import org.apache.flink.annotation.Internal;
import org.apache.flink.core.memory.DataInputView;
import org.apache.flink.core.memory.DataOutputView;
import org.apache.flink.util.InstantiationUtil;

import java.io.IOException;

import static org.apache.flink.util.Preconditions.checkNotNull;
import static org.apache.flink.util.Preconditions.checkState;

/**
 * Base {@link TypeSerializerSnapshot} for serializers for generic types.
 *
 * @param <T> The type to be instantiated.
 */
@Internal
public abstract class GenericTypeSerializerSnapshot<T, S extends TypeSerializer> implements TypeSerializerSnapshot<T> {

	private static final int VERSION = 2;
	private Class<T> typeClass;

	protected GenericTypeSerializerSnapshot() {
	}

	protected GenericTypeSerializerSnapshot(Class<T> typeClass) {
		this.typeClass = checkNotNull(typeClass, "type class can not be NULL");
	}

	/**
	 * Create a serializer that is able to serialize the generic type {@code typeClass}.
	 */
	protected abstract TypeSerializer<T> createSerializer(Class<T> typeClass);

	/**
	 * Gets the type class from the corresponding serializer.
	 */
	protected abstract Class<T> getTypeClass(S serializer);

	/**
	 * Gets the serializer's class.
	 */
	protected abstract Class<?> serializerClass();

	@Override
	public final int getCurrentVersion() {
		return VERSION;
	}

	@Override
	public final void writeSnapshot(DataOutputView out) throws IOException {
		checkState(typeClass != null, "type class can not be NULL");
		out.writeUTF(typeClass.getName());
	}

	@Override
	public final void readSnapshot(int readVersion, DataInputView in, ClassLoader userCodeClassLoader) throws IOException {
		typeClass = InstantiationUtil.resolveClassByName(in, userCodeClassLoader);
	}

	@Override
	@SuppressWarnings("unchecked")
	public final TypeSerializer<T> restoreSerializer() {
		checkState(typeClass != null, "type class can not be NULL");
		return createSerializer(typeClass);
	}

	@Override
	public final TypeSerializerSchemaCompatibility<T> resolveSchemaCompatibility(TypeSerializer<T> newSerializer) {
		if (!serializerClass().isInstance(newSerializer)) {
			return TypeSerializerSchemaCompatibility.incompatible();
		}
		@SuppressWarnings("unchecked") S casted = (S) newSerializer;
		if (typeClass == getTypeClass(casted)) {
			return TypeSerializerSchemaCompatibility.compatibleAsIs();
		}
		else {
			return TypeSerializerSchemaCompatibility.incompatible();
		}
	}
}

Add a generic type snapshot base