This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Since RESTful services are based on HTTP methods, all you need are the standard library java.net.HttpURLConnection and related classes to create a HTTP POST request to the URL of the service with the body of the request containing the text of the XML document.
Nothing magic about it - so much simpler than SOAP.
Of course the various toolkits for RESTful services contain examples, but the client side is always very simple.