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KafkaMessageEnumerator.java
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KafkaMessageEnumerator.java
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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.calcite.adapter.kafka;
import org.apache.calcite.linq4j.Enumerator;
import org.apache.kafka.clients.consumer.Consumer;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import java.time.Duration;
import java.util.LinkedList;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* Enumerator to read data from {@link Consumer},
* and converted into SQL rows with {@link KafkaRowConverter}.
* @param <K>: type for Kafka message key,
* refer to {@link ConsumerConfig#KEY_DESERIALIZER_CLASS_CONFIG};
* @param <V>: type for Kafka message value,
* refer to {@link ConsumerConfig#VALUE_DESERIALIZER_CLASS_CONFIG};
*/
public class KafkaMessageEnumerator<K, V> implements Enumerator<Object[]> {
final Consumer consumer;
final KafkaRowConverter<K, V> rowConverter;
private final AtomicBoolean cancelFlag;
//runtime
private final LinkedList<ConsumerRecord<K, V>> bufferedRecords = new LinkedList<>();
private ConsumerRecord<K, V> curRecord;
KafkaMessageEnumerator(final Consumer consumer,
final KafkaRowConverter<K, V> rowConverter,
final AtomicBoolean cancelFlag) {
this.consumer = consumer;
this.rowConverter = rowConverter;
this.cancelFlag = cancelFlag;
}
/**
* It returns an Array of Object, with each element represents a field of row.
*/
@Override public Object[] current() {
return rowConverter.toRow(curRecord);
}
@Override public boolean moveNext() {
if (cancelFlag.get()) {
return false;
}
while (bufferedRecords.isEmpty()) {
pullRecords();
}
curRecord = bufferedRecords.removeFirst();
return true;
}
private void pullRecords() {
ConsumerRecords<K, V> records = consumer.poll(Duration.ofMillis(100));
for (ConsumerRecord record : records) {
bufferedRecords.add(record);
}
}
@Override public void reset() {
this.bufferedRecords.clear();
pullRecords();
}
@Override public void close() {
consumer.close();
}
}
// End KafkaMessageEnumerator.java