I am getting Internal Server500 error while using DOM parser classes in OAF

// import statements
<%@ page import= "java.io.File"%>
<%@ page import= "java.io.FileOutputStream"%>
<%@ page import= "java.io.IOException"%>
<%@ page import= "javax.xml.parsers.DocumentBuilder"%>
<%@ page import= "javax.xml.parsers.DocumentBuilderFactory"%>
<%@ page import= "javax.xml.parsers.ParserConfigurationException"%>
<%@ page import= "javax.xml.transform.OutputKeys"%>
<%@ page import= "javax.xml.transform.Transformer"%>
<%@ page import= "javax.xml.transform.TransformerConfigurationException"%>
<%@ page import= "javax.xml.transform.TransformerException"%>
<%@ page import= "javax.xml.transform.TransformerFactory"%>
<%@ page import= "javax.xml.transform.dom.DOMSource"%>
<%@ page import= "javax.xml.transform.stream.StreamResult"%>
<%@ page import= "org.w3c.dom.Document"%>
<%@ page import= "org.w3c.dom.Element"%>
<%@ page import= "org.w3c.dom.Node"%>
<%@ page import= "org.w3c.dom.NodeList"%>
 
//code to write xml file
 
  try{
			DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
			DocumentBuilder builder = factory.newDocumentBuilder();
			Document document = builder.newDocument();
			Element rootElement = document.createElement("DashbUnit");
			rootElement.setAttribute("id",dbUnitId);
			document.appendChild(rootElement);
			for(int i=0;i<counter;i++){
				Element setElement1 = document.createElement("Param");
				setElement1.setAttribute("name",parNames[i]);
				setElement1.setAttribute("value",parVals[i]);
				rootElement.appendChild(setElement1);
			}
			TransformerFactory tFactory = TransformerFactory.newInstance();
			
			Transformer transformer = tFactory.newTransformer();
			//Add indentation to output
			transformer.setOutputProperty
			(OutputKeys.INDENT, "yes");
			transformer.setOutputProperty(
					"{http://xml.apache.org/xslt}indent-amount", "2");
			
			DOMSource source = new DOMSource(document);
 
			FileOutputStream output = new FileOutputStream(new File(fPathParVal));
			StreamResult result = new StreamResult(output);
			transformer.transform(source, result);
      System.out.println("file transfered");
			output.flush();
			output.close();
		} catch (IOException e) {
			System.out.println("IOException " + e.getMessage());
		} catch (ParserConfigurationException e) {
			System.out
			.println("ParserConfigurationException " + e.getMessage());
		} catch (TransformerConfigurationException e) {
			System.out.println("TransformerConfigurationException "+ e.getMessage());
		} catch (TransformerException e) {
			System.out.println("TransformerException " + e.getMessage());
		}

                                  

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