kafka Aggregator 源码
kafka Aggregator 代码
文件路径：/streams/src/main/java/org/apache/kafka/streams/kstream/Aggregator.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;
/**
* The {@code Aggregator} interface for aggregating values of the given key.
* This is a generalization of {@link Reducer} and allows to have different types for input value and aggregation
* result.
* {@code Aggregator} is used in combination with {@link Initializer} that provides an initial aggregation value.
* <p>
* {@code Aggregator} can be used to implement aggregation functions like count.
* @param <K> key type
* @param <V> input value type
* @param <VA> aggregate value type
* @see Initializer
* @see KGroupedStream#aggregate(Initializer, Aggregator)
* @see KGroupedStream#aggregate(Initializer, Aggregator, Materialized)
* @see TimeWindowedKStream#aggregate(Initializer, Aggregator)
* @see TimeWindowedKStream#aggregate(Initializer, Aggregator, Materialized)
* @see SessionWindowedKStream#aggregate(Initializer, Aggregator, Merger)
* @see SessionWindowedKStream#aggregate(Initializer, Aggregator, Merger, Materialized)
* @see Reducer
*/
public interface Aggregator<K, V, VA> {
/**
* Compute a new aggregate from the key and value of a record and the current aggregate of the same key.
*
* @param key the key of the record
* @param value the value of the record
* @param aggregate the current aggregate value
* @return the new aggregate value
*/
VA apply(final K key, final V value, final VA aggregate);
}
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