streams/src/main/java/org/apache/kafka/streams/kstream/internals/WindowedStreamPartitioner.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.kafka.streams.kstream.internals;

import org.apache.kafka.common.utils.Utils;
import org.apache.kafka.streams.kstream.Windowed;
import org.apache.kafka.streams.processor.StreamPartitioner;

public class WindowedStreamPartitioner<K, V> implements StreamPartitioner<Windowed<K>, V> {

    private final WindowedSerializer<K> serializer;

    public WindowedStreamPartitioner(WindowedSerializer<K> serializer) {
        this.serializer = serializer;
    }

    /**
     * WindowedStreamPartitioner determines the partition number for a message with the given windowed key and value
     * and the current number of partitions. The partition number id determined by the original key of the windowed key
     * using the same logic as DefaultPartitioner so that the topic is partitioned by the original key.
     *
     * @param windowedKey the key of the message
     * @param value the value of the message
     * @param numPartitions the total number of partitions
     * @return an integer between 0 and {@code numPartitions-1}, or {@code null} if the default partitioning logic should be used
     */
    public Integer partition(Windowed<K> windowedKey, V value, int numPartitions) {
        byte[] keyBytes = serializer.serializeBaseKey(null, windowedKey);

        // hash the keyBytes to choose a partition
        return toPositive(Utils.murmur2(keyBytes)) % numPartitions;
    }

    private static int toPositive(int number) {
        return number & 0x7fffffff;
    }

}