storm-core/src/jvm/org/apache/storm/state/BaseBinaryStateIterator.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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.storm.state;

import com.google.common.collect.Iterators;
import com.google.common.primitives.UnsignedBytes;

import java.util.Iterator;
import java.util.Map;
import java.util.TreeSet;

/**
 * Base implementation of iterator over {@link KeyValueState} which encoded types of key and value are both binary type.
 */
public abstract class BaseBinaryStateIterator<K, V> extends BaseStateIterator<K, V, byte[], byte[]> {

    /**
     * Constructor.
     *
     * @param pendingPrepareIterator The iterator of pendingPrepare
     * @param pendingCommitIterator The iterator of pendingCommit
     */
    public BaseBinaryStateIterator(Iterator<Map.Entry<byte[], byte[]>> pendingPrepareIterator,
                                   Iterator<Map.Entry<byte[], byte[]>> pendingCommitIterator) {
        super(Iterators.peekingIterator(pendingPrepareIterator), Iterators.peekingIterator(pendingCommitIterator),
                new TreeSet<>(UnsignedBytes.lexicographicalComparator()));
    }

    /**
     * Load some part of state KVs from storage and returns iterator of cached data from storage.
     *
     * @return Iterator of loaded state KVs
     */
    protected abstract Iterator<Map.Entry<byte[], byte[]>> loadChunkFromStateStorage();

    /**
     * Check whether end of data is reached from storage state KVs.
     *
     * @return whether end of data is reached from storage state KVs
     */
    protected abstract boolean isEndOfDataFromStorage();

    /**
     * Decode key to convert byte array to state key type.
     *
     * @param key byte array encoded key
     * @return Decoded value of key
     */
    protected abstract K decodeKey(byte[] key);

    /**
     * Decode value to convert byte array to state value type.
     *
     * @param value byte array encoded value
     * @return Decoded value of value
     */
    protected abstract V decodeValue(byte[] value);

    /**
     * Check whether the value is tombstone (deletion mark) value.
     *
     * @param value the value to check
     * @return true if the value is tombstone, false otherwise
     */
    protected abstract boolean isTombstoneValue(byte[] value);

}