THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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The Camel API is influenced by APIs such as JBI specification, CXF which defines a concept called Message Exchange Patterns (MEP for short).
The MEP defines the messaging style used such as one-way (InOnly) or request-reply (InOut),
which means you have IN and optionally OUT messages. This closely maps to other APIs such as WS, WSDL, REST, JBI and the likes.
The Exchange API provides two methods to get a message, either getIn or getOut.
Obviously the getIn gets the IN message, and the getOut gets the OUT message.
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This seems intuitive and is what you would expect is the right approach to change a message from a Processor.
However there is an big issue - the getOut method will create a new Message, which means any other information
from the IN message will not be propagated; which means you will lose that data.
To remedy this we'll have to copy the data
which is done as follows:
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As shown above you most often need to alter the existing IN message, than creating a totally new OUT message. |
Changing the IN message directly is possible in Camel as it don't mind. Camel will detect that the Exchange has no OUT message
and therefore use the IN message instead.
About Message Exchange Pattern and getOut
If the Exchange is using InOnly as the MEP, then you may think that the Exchange has no OUT message.
But you can still invoke the getOut method on Exchange; Camel will not barf.
So the example code above is possible for any kind of MEP. The MEP is just a flag on the Exchange which the Consumer and Producer adhere to.
You can change the MEP on the Exchange using the setPattern method. And likewise there is DSL to change it as well.