public Node getChildNode(Document doc, Node father, String tagName){
		
		Node childNode = null;
		NodeList nodeList = doc.getElementsByTagName(tagName);
		if(nodeList.getLength() > 0){
			for(int i=0;i<nodeList.getLength();i++){
				Node node = nodeList.item(i);
				if(node.getParentNode().equals(father)){
					childNode = node;
				}
			}
		}
		
		return childNode;
	}