The content-type is set to the content type of the encoder. See here:

For the xml encoder that is "application/xml". See here (the first entry in the list is taken to be the default content-type):

Your best bet is to enable debugging in the apache http client to see what is actually being sent. You can do this by setting the system properties correctly. See here for the details on how to do this:

On Tue, Jun 7, 2016 at 8:15 AM, Imholz, John J. <> wrote:
I'd like to set the Content-type of a POST to "text/xml"  looks to me like http.request( POST, XML)  sets it to "application/xml".

Also, to debug, how can I see the POST before I send it?