How to aggregate messages with the identical headers in Spring Integration - spring

Question

public static void main(String[] args) throws InterruptedException {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.register(Main.class);
ctx.refresh();
DirectChannel channel1 = ctx.getBean("channel1", DirectChannel.class);
ctx.getBean("channel2", PublishSubscribeChannel.class).subscribe(message ->
System.out.println("Output: " + message));
channel1.send(MessageBuilder.withPayload("p1")
.setHeader(CORRELATION_ID, 1)
.setHeader(SEQUENCE_SIZE,2)
.setHeader(SEQUENCE_NUMBER,1)
.setHeader("a", 1)
.build());
channel1.send(MessageBuilder.withPayload("p2")
.setHeader(CORRELATION_ID, 1)
.setHeader(SEQUENCE_SIZE,2)
.setHeader(SEQUENCE_NUMBER,2)
.setHeader("a", 2)
.build());
}
#Bean
public MessageChannel channel1() {
return MessageChannels.direct().get();
}
#Bean
public MessageChannel channel2() {
return MessageChannels.publishSubscribe().get();
}
#Bean
public IntegrationFlow flow1() {
return IntegrationFlows
.from("channel1")
.aggregate(a -> a
.releaseStrategy(new SequenceSizeReleaseStrategy())
.expireGroupsUponCompletion(true)
.sendPartialResultOnExpiry(true))
.channel("channel2")
.get();
}
Output: GenericMessage [payload=[p1, p2], headers={sequenceNumber=2, a=2, correlationId=1, id=b5e51041-c967-1bb4-1601-7e468ae28527, sequenceSize=2, timestamp=1580475773518}]
Headers "a" and "sequenceNumber" were overwritten.
How to aggregate messages with the identical headers?
It must be so
Output: GenericMessage [payload=[p1, p2], headers={sequenceNumber=[1,2], a=[1, 2], correlationId=1, id=b5e51041-c967-1bb4-1601-7e468ae28527, sequenceSize=2, timestamp=1580475773518}]

Answer 1

See AbstractAggregatingMessageGroupProcessor:
/**
* Specify a {#link Function} to map {#link MessageGroup} into composed headers for output message.
* #param headersFunction the {#link Function} to use.
* #since 5.2
*/
public void setHeadersFunction(Function<MessageGroup, Map<String, Object>> headersFunction) {
and also:
/**
* The {#link Function} implementation for a default headers merging in the aggregator
* component. It takes all the unique headers from all the messages in group and removes
* those which are conflicted: have different values from different messages.
*
* #author Artem Bilan
*
* #since 5.2
*
* #see AbstractAggregatingMessageGroupProcessor
*/
public class DefaultAggregateHeadersFunction implements Function<MessageGroup, Map<String, Object>> {
Or just long existing:
/**
* This default implementation simply returns all headers that have no conflicts among the group. An absent header
* on one or more Messages within the group is not considered a conflict. Subclasses may override this method with
* more advanced conflict-resolution strategies if necessary.
* #param group The message group.
* #return The aggregated headers.
*/
protected Map<String, Object> aggregateHeaders(MessageGroup group) {
So, what you need in your aggregate() configuration is an outputProcessor(MessageGroupProcessor outputProcessor) option.
See docs for more info: https://docs.spring.io/spring-integration/docs/5.2.3.RELEASE/reference/html/message-routing.html#aggregatingmessagehandler