Handlers can be used to do all sorts of things with XFire. They can process the SOAP Body or they can process a particular header and take action based on it. To write a handler just extend the AbstractHandler class:
Handlers can be registered with a Service or a Transport. On both Services and Transports you can stick a handler in a request or response pipeline:
Processing SOAP Headers
If you are using the "mustUnderstand" feature of SOAP you must tell XFire which QNames you can handle: