package mypackage;

public abstract class myXML {
	
    public static String setvalue(String xml, String element, String Value) {
    	try {
    		XPath xpath = XPathFactory.newInstance().newXPath();
    		NodeList nl = (NodeList) xpath.evaluate(element, new InputSource(new StringReader(xml)), XPathConstants.NODESET);
    	
    		if (nl.getLength() ==  1 ) {
    			nl.item( 0 ).setNodeValue(Value);
    			
    			StringWriter writer = new StringWriter();
    	        TransformerFactory.newInstance().newTransformer().transform(
    	                new DOMSource(nl.item( 0 ).getOwnerDocument()),
    	                new StreamResult(writer));
    	        
    	        return writer.toString();
    		}
    	} catch (Exception e) {
    	}
    	return null;
    }
}

CREATE OR REPLACE FUNCTION xml_set_value (p_xml varchar, p_element varchar, p_value varchar) RETURNS varchar AS
$body$
mypackage.myXML.setvalue
$body$
LANGUAGE 'java';

SELECT xml_set_value(contacts, '/contacts/tel/mobile/text()', '888-444-4444') FROM users.users;