spring-kafka MessagingTransformer 源码
spring-kafka MessagingTransformer 代码
文件路径:/spring-kafka/src/main/java/org/springframework/kafka/streams/messaging/MessagingTransformer.java
/*
* Copyright 2019-2022 the original author or authors.
*
* Licensed 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
*
* https://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.springframework.kafka.streams.messaging;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.producer.ProducerRecord;
import org.apache.kafka.common.header.Headers;
import org.apache.kafka.common.record.TimestampType;
import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.kstream.Transformer;
import org.apache.kafka.streams.processor.ProcessorContext;
import org.springframework.kafka.support.KafkaHeaders;
import org.springframework.kafka.support.converter.MessagingMessageConverter;
import org.springframework.messaging.Message;
import org.springframework.util.Assert;
/**
* A {@link Transformer} implementation that invokes a {@link MessagingFunction}
* converting to/from spring-messaging {@link Message}. Can be used, for example,
* to invoke a Spring Integration flow.
*
* @param <K> the key type.
* @param <V> the value type.
* @param <R> the result value type.
*
* @author Gary Russell
* @since 2.3
*
*/
public class MessagingTransformer<K, V, R> implements Transformer<K, V, KeyValue<K, R>> {
private final MessagingFunction function;
private final MessagingMessageConverter converter;
private ProcessorContext processorContext;
/**
* Construct an instance with the provided function and converter.
* @param function the function.
* @param converter the converter.
*/
public MessagingTransformer(MessagingFunction function, MessagingMessageConverter converter) {
Assert.notNull(function, "'function' cannot be null");
Assert.notNull(converter, "'converter' cannot be null");
this.function = function;
this.converter = converter;
}
@Override
public void init(ProcessorContext context) {
this.processorContext = context;
}
@SuppressWarnings({ "unchecked", "rawtypes" })
@Override
public KeyValue<K, R> transform(K key, V value) {
Headers headers = this.processorContext.headers();
ConsumerRecord<Object, Object> record = new ConsumerRecord<Object, Object>(this.processorContext.topic(),
this.processorContext.partition(), this.processorContext.offset(),
this.processorContext.timestamp(), TimestampType.NO_TIMESTAMP_TYPE,
0, 0,
key, value,
headers, Optional.empty());
Message<?> message = this.converter.toMessage(record, null, null, null);
message = this.function.exchange(message);
List<String> headerList = new ArrayList<>();
headers.forEach(header -> headerList.add(header.key()));
headerList.forEach(name -> headers.remove(name));
ProducerRecord<?, ?> fromMessage = this.converter.fromMessage(message, "dummy");
fromMessage.headers().forEach(header -> {
if (!header.key().equals(KafkaHeaders.TOPIC)) {
headers.add(header);
}
});
Object key2 = message.getHeaders().get(KafkaHeaders.KEY);
return new KeyValue(key2 == null ? key : key2, message.getPayload());
}
@Override
public void close() {
// NO-OP
}
}
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