I'm afraid you had to use the "Content-Type" directly as current Spring DSL doesn't support to reference the constance from class directly.
Maybe we could introduce some syntax for that, so Camel can evaluate on startup the header name is spelt correctly?
<setHeader headerName="Exchange.CONTENT_TYPE"> ... </setHeader>
Either Camel detects that you have typed a constant field name from the Exchange interface and will lookup the value of that constant and use it.
However what about other constants? Maybe we need a special syntax to tell Camel that it's a constant?
Or maybe we don't need it if Camel can resolve that into a constant on an interface/class and just use it?