Oracle Forms

I have went through oracle's demo on calling a web service in forms, but now I want to call a different web service. I have set up everything just like the demo, but I am not sure how to code the call from the when-button-pressed I have the following code so far ( from the demo):
DECLARE
jo ora_java.jobject;
rv ora_java.jobject;
ex ora_java.jobject;
BEGIN
Jo := HELLOWSSTUB.new;
--

--
rv := HELLOWSSTUB.sayHelloWorld(jo,':Name');
-- message (float_.floatValue(rv));
/*EXCEPTION
WHEN ORA_JAVA.JAVA_ERROR then
message('Unable to call out to Java, ' ||ORA_JAVA.LAST_ERROR);
WHEN ORA_JAVA.EXCEPTION_THROWN then
ex := ORA_JAVA.LAST_EXCEPTION;
message(Exception_.toString(ex));*/
END;essed trigger.