Hi Claus,
Thanks for the explanation. I have two related questions.
1. For consistency in testing, it seems like
MockEndpoint.extractActualValue() should also not evaluate the Expression.
2. Would it make sense in setHeader() to throw an exception if the value
is of type Expression since it will not be evaluated? Or would this also
add too much overhead?
Karen Lease
On 29/08/2021 16:27, Claus Ibsen wrote:
Hi
This is not a bug, or something like that.
When you use a Processor then its "normal" java code you write there,
so setting a message header, og body or exchange property, then you
set the value as-is, eg its a Object type.
This is by design, as its just normal Java. What you set is what is used.
The underlying code in DefaultMessage / DefaultExchange is also
optimized for these situations to be as fast and low overhead as
possible, especially due to that setting headers is frequently used,
eg a component consumer sets a set of meta-data headers when a new
message is received.
On the other hand when you program in the RouteBuilder, then you
"design" a Camel route (in the configure method). The code there is a
"plan" where you need to use constant / simple / and whatnot to tell
Camel the plan.
In the case of "constant" then that is actually a corner case, as you
could argue that constant(500) can be inferred when doing the "plan"
as 500 is the constant value you want to use.
So suppose if you could say
.setHeader("foo", 500) in the RouteBuilder then Camel could infer that
500 will be a constant. However using constant is not so common in
use, and to make the "plan" consistent, then you need to use an
Expression, just as you would when you use
setHeader("foo", simple( .... ))
Or if you use json-path / xpath
setHeader("foo", xpath("/myroot/mynode@city"))
The problem you hit was that your Processor is anonymous inside the
RouteBuilder so it "inherits" the route builder methods where constant
is available and you mistakenly use that.
If the Processor is not anonymous by a top level class then you could
not do that as it does not extend from RouteBuilder.
