XPathFactory factory = XPathFactory.newInstance();
XPath xpath = factory.newXPath();
factory.setXPathFunctionResolver(new MyFunctionResolver());
xpath.setNamespaceContext(new MyNamespaceContext());
xpath.setXPathFunctionResolver(new MyFunctionResolver());
 
XPathExpression expr = xpath.compile(str);
String result = expr.evaluate(doc); 
System.out.println(result);

public Object evaluate(java.util.List args) 
{
	System.out.println("Inside evaluate");
	if (args.size() == 2) {
	
        return new String(args.get(0).toString() 
                          + " , " + 
                          args.get(1).toString());	
 
	}
}