Camel Inter module coordination - dependency - apache-camel

Question

My problem is I have a routeBuilder which does routing based on url patterns to different modules say A, B, D as follows (the customProcessor adds the ARestURN, BRestURN etc to the header which are comma seperated url patterns that will be matched against the in header CamelHttpUri to route to correct module)
from("servlet:///?matchOnUriPrefix=true")
.process(customProcessor)
.choice()
.when(simple("${in.headers.ARestURN} contains ${in.headers.CamelHttpUri}"))
.to("http4://" + AUrl + "?bridgeEndpoint=true&throwExceptionOnFailure=false")
.when(simple("${in.headers.BRestURN} contains ${in.headers.CamelHttpUri}"))
.to("http4://" + BUrl + "?bridgeEndpoint=true&throwExceptionOnFailure=false")
.otherwise()
.to("http4://" + DUrl + "?bridgeEndpoint=true&throwExceptionOnFailure=false");
My question is now I need to service a REST url request which requires me to acccess AUrl and BUrl and aggregate the results and then respond to the request how do I achieve this ?
I thought of writing something as below
from("servlet:///?matchOnUriPrefix=true")
.process(customProcessor)
.choice()
.when(simple("${in.headers.ARestURN} contains ${in.headers.CamelHttpUri}"))
.to("http4://" + AUrl + "?bridgeEndpoint=true&throwExceptionOnFailure=false")
.when(simple("${in.headers.BRestURN} contains ${in.headers.CamelHttpUri}"))
.to("http4://" + BUrl + "?bridgeEndpoint=true&throwExceptionOnFailure=false")
.when(simple("${in.headers.MultiModuleRestURN} contains ${in.headers.CamelHttpUri}"))
.to("direct:multimodule")
.otherwise()
.to("http4://" + DUrl + "?bridgeEndpoint=true&throwExceptionOnFailure=false");
from("direct:multimodule")
.process(new MyProcessor())
.to("http4://" + AUrl + "?bridgeEndpoint=true&throwExceptionOnFailure=false");
But I don't get howto get the results from first "AUrl" (which is a REST service returning json results) and do some process on it and provide specific values of the result to the next url which is BUrl to get results from it and process that and combine results and send it back to the calling service.
eg:
the REST call : /AB/123/getPrice
Need to pass 123 to Module A - REST call -> /A/123/getId response-{A: 123, id: x1}
Need to pass x1 to Module B - REST call -> /B/x1/getPrice response-{id: x1, p:$10}
Need to return to caller {name: 123, id: x1, price: $10 } (json combined object)
Update: Did as follows for now,
Note: removed bridgeEndpoint stuff for clarity
from("servlet:///?matchOnUriPrefix=true")
.process(customProcessor)
.choice()
.when(simple("${in.headers.multiRestURN} contains ${in.headers.CamelHttpUri}"))
.to("direct:multimodule")
.when(simple("${in.headers.ARestURN} contains ${in.headers.CamelHttpUri}"))
.to("http4://" +AUrl)
.when(simple("${in.headers.BRestURN} contains ${in.headers.CamelHttpUri}"))
.to("http4://" +BUrl)
.otherwise()
.to("http4://" +DUrl);
//
from("direct:multimodule")
.to(ExchangePattern.InOut,"http4://"+AUrl)
.convertBodyTo(String.class)
.process(customAProcess)
.to(ExchangePattern.InOut, "http4://"+BUrl+"/resources")
.convertBodyTo(String.class)
.process(customBProcessor);
In customAProcess I do a
exchange.getIn().setHeader("AData", exchange.getIn().getBody(String.class));
So this data is available when BUrl request comes with result, I am sending to BUrl unnecessary data but this solves the issue hopefully, maybe when I get time I will look into enricher and aggregate strategy to solve the issue.

Answer 1

Enricher component might be what you are looking for. It's implementation of one of common patters. Please, note that it is possible to pass implementation of aggregation strategy via strategyRef parameter.
While implementing aggregation strategy for your first rest call you are able to enrich original exchange by returned data of your first rest response - see interface of AggregationStrategy, please. Just create beans of your strategies and configure enricher.
Hope it helps. Example context :) :
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
<route>
<from uri="servlet:///?matchOnUriPrefix=true"/>
<enrich uri="http4://serviceA" strategyRef="strategyA"/>
<enrich uri="http4://serviceB" strategyRef="strategyB"/>
</route>
</camelContext>
<bean id="strategyA" class="..." />
<bean id="strategyB" class="..." />
You can do whatever you want with your exchanges, both original (being enriched) and new (enriching) in aggregation strategies.