This logic was lifted from the original method MessageBusSupport.resolveContentType(), a private method used only to support serialization internally. The message bus saves the original content type in a message header, replaces the contentType header and then restores it to its original value during deserialization.  So APPLICATION_OCTET_STREAM is used simply to indicate the payload is already a byte[] and does not require deserialization . MBS used the static imports where these constants are used in many places, so preserved in this class. I agree, not that useful in this case.