Here is Stuarts response from a similar question.

You need to implement org.xnio.conduits.StreamSinkConduit and add io.undertow.server.HttpServerExchange#addResponseWrapper

There is no simple in memory representation of the response, because it may be to large for the server to buffer (or more likely the server does not want to buffer it for performance reasons). Implementing this will allow you to modify the response as it is being written.


Stuart