MessageFormatter implementations are used by Axis2 to support serialization
of messages to different message formats. (Eg: JSON). Users can register
MessageFormatter implementations against a message type using the axis2.xml.
Message type for a message can be specified by setting the "messageType"
property in the MessageContext. This can also be given as a parameter in the
service.xml/axis2.xml for a per service based/engine wide configuration.
To support deffered writing transports as in http chunking.. Axis2 was
doing this for some time..
Preserve flag can be used to preserve the envelope for later use. This is
usefull when implementing authentication machnisms like NTLM.
preserve - :
do not consume the OM when this is set..