My boss has said to me that make User interface from that UI you select the wsdl web service loc and you get all available method in an combo box and on selection of an method from the combo box you get all the input text fields. then on ok button you get the response from the integration layer(ws side).
Both Eclipse and GlassFish have web service testers and they are open source, as is soapUI that has been mentioned earlier.
Digging around in their source may perhaps give you some clues on how to proceed (which perhaps is what mr Dittmer already said...).
Just a thought...