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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.flink.runtime.state;

import org.apache.flink.core.fs.FSDataInputStream;
import org.apache.flink.core.fs.Path;
import org.apache.flink.runtime.state.filesystem.FileStateHandle;
import org.apache.flink.util.InstantiationUtil;
import org.apache.flink.util.Preconditions;

import java.io.Closeable;
import java.io.IOException;
import java.io.Serializable;
import java.util.Optional;

/**
 * Wrapper around a {@link StreamStateHandle} to make the referenced state object retrievable trough
 * a simple get call. This implementation expects that the object was serialized through default
 * serialization of Java's {@link java.io.ObjectOutputStream}.
 *
 * @param  type of the retrievable object which is stored under the wrapped stream handle
 */
public class RetrievableStreamStateHandle
        implements StreamStateHandle, RetrievableStateHandle, Closeable {

    private static final long serialVersionUID = 314567453677355L;

    /** wrapped inner stream state handle from which we deserialize on retrieval */
    private final StreamStateHandle wrappedStreamStateHandle;

    public RetrievableStreamStateHandle(StreamStateHandle streamStateHandle) {
        this.wrappedStreamStateHandle = Preconditions.checkNotNull(streamStateHandle);
    }

    public RetrievableStreamStateHandle(Path filePath, long stateSize) {
        Preconditions.checkNotNull(filePath);
        this.wrappedStreamStateHandle = new FileStateHandle(filePath, stateSize);
    }

    @Override
    public T retrieveState() throws IOException, ClassNotFoundException {
        try (FSDataInputStream in = openInputStream()) {
            return InstantiationUtil.deserializeObject(
                    in, Thread.currentThread().getContextClassLoader());
        }
    }

    @Override
    public FSDataInputStream openInputStream() throws IOException {
        return wrappedStreamStateHandle.openInputStream();
    }

    @Override
    public Optional asBytesIfInMemory() {
        return wrappedStreamStateHandle.asBytesIfInMemory();
    }

    @Override
    public void discardState() throws Exception {
        wrappedStreamStateHandle.discardState();
    }

    @Override
    public long getStateSize() {
        return wrappedStreamStateHandle.getStateSize();
    }

    @Override
    public void close() throws IOException {
        //		wrappedStreamStateHandle.close();
    }
}