How to pass information between spring-integration components? - spring-integration

Question

In spring-batch, data can be passed between various steps via ExecutionContext. You can set the details in one step and retrieve in the next. Do we have anything of this sort in spring-integration ?
My use case is that I have to pick up a file from ftp location, then split it based on certain business logic and then process them. Depending on the file names client id would be derived. This client id would be used in splitter, service activator and aggregator components.
From my newbie level of expertise I have in spring, I could not find anything which help me share state for a particular run.I wanted to know if spring-integration provides this state sharing context in some way.
Please let me know if there is a way to do in spring-context.

Answer 1

In Spring Integration applications there is no single ExecutionContext for state sharing. Instead, as Gary Russel mentioned, each message carries all the information within its payload or its headers.
If you use Spring Integration Java DSL and want to transport the clientId by message header you can use enrichHeader transformer. Being supplied with a HeaderEnricherSpec, it can accept a function which returns dynamically determined value for the specified header. As of your use case this might look like:
return IntegrationFlows
.from(/*ftp source*/)
.enrichHeaders(e -> e.headerFunction("clientId", this::deriveClientId))
./*split, aggregate, etc the file according to clientId*/
, where deriveClientId method might be a sort of:
private String deriveClientId(Message<File> fileMessage) {
String fileName = fileMessage.getHeaders().get(FileHeaders.FILENAME, String.class);
String clientId = /*some other logic for deriving clientId from*/fileName;
return clientId;
}
(FILENAME header is provided by FTP message source)
When you need to access the clientId header somewhere in the downstream flow you can do it the same way as file name mentioned above:
String clientId = message.getHeaders().get("clientId", String.class);
But make sure that the message still contains such header as it could have been lost somewhere among intermediate flow items. This is likely to happen if at some point you construct a message manually and send it further. In order not to loose any headers from the preceding message you can copy them during the building:
Message<PayloadType> newMessage = MessageBuilder
.withPayload(payloadValue)
.copyHeaders(precedingMessage.getHeaders())
.build();
Please note that message headers are immutable in Spring Integration. It means you can't just add or change a header of the existing message. You should create a new message or use HeaderEnricher for that purpose. Examples of both approaches are presented above.

Answer 2

Typically you convey information between components in the message payload itself, or often via message headers - see Message Construction and Header Enricher