pulsar-flink/src/main/java/org/apache/flink/streaming/connectors/pulsar/partitioner/PulsarKeyExtractor.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.streaming.connectors.pulsar.partitioner;

import java.io.Serializable;

/**
 * Extract key from a value.
 */
public interface PulsarKeyExtractor<T> extends Serializable {

    PulsarKeyExtractor NULL = in -> null;

    /**
     * Retrieve a key from the value.
     *
     * @param in the value to extract a key.
     * @return key.
     */
    String getKey(T in);

}