Question

Given a xml file as input howto modify a attribute of a tag with a new string value?

Function is

updateXMLAttribute(Document doc , String tag, String attribute, String newValue){

//impl

}

How can i do it?

Answer 1

I assume, by Document you mean org.w3c.dom.Document:

updateXMLAttribute(Document doc , String tag, String attribute, String newValue) {
   NodeList nodes = doc.getElementsByTagName(tag);
   for(int i=0; i<nodes.getLength(); i++) {
       if(nodes.item(i) instanceof Element) {
           Element elem = (Element)nodes.item(i);
           Attr attribute = elem.getAttributeNode(attribute);
           attribute.setValue(newValue);
       }
   }
}

This will update all attribute values of attributes named in elements named in a dom document.
Of course, you should add appropriate error handling and null-checks.

PS: You can find all the information in the dom api documentation: http://www.w3.org/2003/01/dom2-javadoc/org/w3c/dom/Document.html