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/*
* Copyright (c) 2010-2018. Axon Framework
* 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
*
* 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.axonframework.kafka.eventhandling;
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.header.internals.RecordHeader;
import org.axonframework.common.Assert;
import org.axonframework.eventhandling.EventMessage;
import org.axonframework.eventhandling.GenericEventMessage;
import org.axonframework.eventhandling.async.SequencingPolicy;
import org.axonframework.eventhandling.async.SequentialPerAggregatePolicy;
import org.axonframework.eventsourcing.GenericDomainEventMessage;
import org.axonframework.messaging.MetaData;
import org.axonframework.serialization.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.time.Instant;
import java.util.Arrays;
import java.util.Optional;
import java.util.function.BiFunction;
import static org.axonframework.kafka.eventhandling.HeaderUtils.*;
import static org.axonframework.messaging.Headers.*;
/**
* Converts: {@link EventMessage} to {@link ProducerRecord kafkaMessage} and {@link ConsumerRecord message read from
* Kafka} back
* to {@link EventMessage} (if possible).
*
* During conversion it passes all meta-data entries with {@code 'axon-metadata-'} prefix to {@link Headers}. Other
* message-specific attributes are added as metadata. The payload is serialized using the
* configured {@link Serializer} and passed as the message body.
*
* This implementation will suffice in most cases.
*
* @author Nakul Mishra
* @since 3.0
*/
public class DefaultKafkaMessageConverter implements KafkaMessageConverter {
private static final Logger logger = LoggerFactory.getLogger(KafkaMessageConverter.class);
private final Serializer serializer;
private final SequencingPolicy> sequencingPolicy;
private final BiFunction headerValueMapper;
/**
* Initializes the KafkaMessageConverter with the given {@code serializer}.
*
* @param serializer The serializer to serialize the Event Message's payload with.
*/
public DefaultKafkaMessageConverter(Serializer serializer) {
this(serializer, SequentialPerAggregatePolicy.instance(), byteMapper());
}
/**
* Initializes the KafkaMessageConverter with the given {@code serializer}, {@code sequencingPolicy} and
* {@code objectMapper}.
*
* @param serializer The serializer to serialize the Event Message's payload and Meta Data with
* @param sequencingPolicy The policy to generate the key of the {@link ProducerRecord}.
* @param headerValueMapper The Function for mapping values to Kafka headers.
*/
public DefaultKafkaMessageConverter(Serializer serializer,
SequencingPolicy> sequencingPolicy,
BiFunction headerValueMapper) {
Assert.notNull(serializer, () -> "Serializer may not be null");
Assert.notNull(sequencingPolicy, () -> "SequencingPolicy may not be null");
Assert.notNull(headerValueMapper, () -> "HeaderValueMapper may not be null");
this.serializer = serializer;
this.sequencingPolicy = sequencingPolicy;
this.headerValueMapper = headerValueMapper;
}
@Override
public ProducerRecord createKafkaMessage(EventMessage eventMessage, String topic) {
SerializedObject serializedObject = eventMessage.serializePayload(serializer, byte[].class);
byte[] payload = serializedObject.getData();
return new ProducerRecord<>(topic,
null,
null,
key(eventMessage),
payload,
toHeaders(eventMessage, serializedObject, headerValueMapper));
}
private String key(EventMessage eventMessage) {
Object identifier = sequencingPolicy.getSequenceIdentifierFor(eventMessage);
return identifier != null ? identifier.toString() : null;
}
@Override
public Optional> readKafkaMessage(ConsumerRecord consumerRecord) {
try {
Headers headers = consumerRecord.headers();
if (isAxonMessage(headers)) {
byte[] messageBody = consumerRecord.value();
SerializedMessage message = extractSerializedMessage(headers, messageBody);
return buildMessage(headers, message);
}
} catch (Exception e) {
logger.trace("Error converting {} to axon", consumerRecord, e);
}
return Optional.empty();
}
private Optional> buildMessage(Headers headers, SerializedMessage message) {
long timestamp = valueAsLong(headers, MESSAGE_TIMESTAMP);
return headers.lastHeader(AGGREGATE_ID) != null ?
domainEvent(headers, message, timestamp) :
event(message, timestamp);
}
private SerializedMessage extractSerializedMessage(Headers headers, byte[] messageBody) {
SimpleSerializedObject serializedObject = new SimpleSerializedObject<>(
messageBody,
byte[].class,
valueAsString(headers, MESSAGE_TYPE),
valueAsString(headers, MESSAGE_REVISION, null)
);
return new SerializedMessage<>(
valueAsString(headers, MESSAGE_ID),
new LazyDeserializingObject<>(serializedObject, serializer),
new LazyDeserializingObject<>(MetaData.from(extractAxonMetadata(headers))));
}
private boolean isAxonMessage(Headers headers) {
return keys(headers).containsAll(Arrays.asList(MESSAGE_ID, MESSAGE_TYPE));
}
private Optional> domainEvent(Headers headers,
SerializedMessage message, long timestamp) {
return Optional.of(new GenericDomainEventMessage<>(valueAsString(headers, AGGREGATE_TYPE),
valueAsString(headers, AGGREGATE_ID),
valueAsLong(headers, AGGREGATE_SEQ),
message, () -> Instant.ofEpochMilli(timestamp)));
}
private Optional> event(SerializedMessage message, long timestamp) {
return Optional.of(new GenericEventMessage<>(message, () -> Instant.ofEpochMilli(timestamp)));
}
}