You can use CXF wsdl2Java to generate a client code for the web service.
Once you run the wsdl2java , you will get a set of java classes generated for you. You can then use those classes to call the services without any explicit conversion of XML - the underlying framework will do it for you automatically. You can start with http://cxf.apache.org/docs/how-do-i-develop-a-client.html
I proposed CXF while you can look for many other alternatives - However, i have found CXF to be very feature rich and will help you in developing/working with web services.