Hi:
The mail tell 3 things:
1) pipeline processor, along with other build-in processor of camel(which
doesn't care MEP) will cause a confusing things;
2) some source code of camel concerned of this confusing.
3) how to understand the confusing things? it concerns of MEP , which has been
discussed again and again. Sometimes I think I understand it, Sometimes it will
confuse me again suddenly;
1)a confusing things of a simple test case:
from("direct:start2")
.multicast(new AggregateBean())
.pipeline().transform(constant(1)).bean(new IncreaseBean()).end()
.pipeline().transform(constant(1)).bean(new IncreaseBean()).end()
.end()
.to("mock:result2");
the two pipeline of multicast does same things: 1+1 = 2; and the multicast's
aggregate will sum the two pipeline's result: that's 2+2 = 4;
So the reasonable result of the route should be 4, but the final result is 2
when using the default MEP(inOnly);
Is it a bug? How could camel to resolve it ?
2) source code concerned with this confuse things
2.1): TransformProcess's source code, it always set output , which doesn't obey
rule's of camel MEP;
Object newBody = expression.evaluate(exchange, Object.class);
exchange.getOut().setBody(newBody);
2.2): source code from pipeline:
if (first) {
first = false;//so the first processor of pipeline will directly change
the exchange.
} else {
// prepare for next run
nextExchange = createNextExchange(nextExchange);
}
the first processor of pipeline will directly change the exchange instance
received by pipeline.
2.3): source code of PipeLine:
ExchangeHelper.copyResults(exchange, nextExchange);
Here, var "exchange" is the original exchange, "nextExchange" will be the last
processor's result;
So at the end of pipeline's process, the original exchange will be used to
calculate the result of pipeline;
Because if the MEP is inOnly , so the bean's result (integer 2) will set to
the in message.But the first processor of pipeline is transform, and it also
directly set out message; so the final result of pipeline is : exchange{in=2,
out=1};
Then the multicast processor is confused, it thinks the out message contains
the result(but actually in message contains), so the aggregate will receive the
number 1(not number 2) as input to sum;
3) confuse things about the problem.
Now the reason of the confusing is clearly, but how to correct it?
It's TransformProcessor's question , PipeLine's question
At first I think it's the TransformProcessor's question, because it doesn't
obey the rule of camel MEP: it should check MEP and return result in out or in
message;
But let's check the source code of Pipeline: 1) in the pipeline, no matter
which MEP is, it always assume out message prior to in message. So if out
message exist ,pipeline will always using the out as next processor's input 2)
No matter what MEP is, if the last processor 's exchange has out, the pipeline
processor will use it's out message as result;
Now a conflict thing occurred:
1)If camel ask for all processor shouldn't return out message in INONLY MEP,
why the camel itself process the Out message in InOnly mep?
Why not just raise a fatal error to say the process shouldn't return out
message in InOnly MEP.
2) if camel allow some processor could return the out message in InOnly MEP for
some special purpose, so what's the special purpose, how to understand it?
