get/set Parmeters of SoapRequest via JAVA

Hi,
i'm writing a java programm that uses the soapUi-Api.
I know how to read WSDLs, how to send requsts and how to read the answer.
However I don't know how to set the Parmeters for a SOAP request.

Lets assume the following Code. How do I set the Parmeters value between the <axis:input></axis:input> tags via the Api?

<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope" xmlns:axis="http://axishotels.de">
   <soap:Header/>
   <soap:Body>
      <axis:getEcho>
         <!--Optional:-->
         <axis:input>MyInput</axis:input>
      </axis:getEcho>
   </soap:Body>
</soap:Envelope>

I'm looking for something like:

WsdlOperation operation = (WsdlOperation) iface.getOperationAt(0);  // load Operation from WSDL
operation.getAttributes();  // read out all parmeters
operation.setAttribute('input') = "myValue" // set parmeter value

Thx
Andy