In order to invoke a webMethods service from within a java service, you would need to use one of the doInvoke (or doThreadInvoke) methods from the Service class.
you can also try this way to call a flow service from java service.
IData out= context.invoke(“namespace”, “service name”, "input);
out : IData where does java store the output of the webMethods service.
namespace : The folder where do you store your service in the webMethods. (eg : “pub.flow”)
service name : Service name which will you call from java code.
input : IData input of the service that want tobe called.