Create a new version of paste:

package model;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.net.URISyntaxException;
import java.net.URL;
import java.util.ArrayList;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import com.sun.org.apache.bcel.internal.util.ClassPath;
import javafx.scene.control.Alert;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

/**
 * The XMLManager class is used to do operations on the XML file
 *
 * @author 2, 3
 */
public class XMLManager
{
    /**
     * the location of the XML file
     */
    private static File userfile = new File("Server/Resources/userlist.xml");


    //gets all the user nodes

    /**
     *
     * @return get a nodelist containing all the users in the XML file
     */
	public static NodeList getUserNodeList(){
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
		DocumentBuilder documentBuilder;
		Document document = null;
        try {
            documentBuilder = documentBuilderFactory.newDocumentBuilder();
            document = documentBuilder.parse(userfile);
            document.getDocumentElement().normalize();
        }
        catch (ParserConfigurationException e) {
            e.printStackTrace();
        }
        catch (IOException ioe) {
            ioe.printStackTrace();
        }
        catch (SAXException sae) {
            sae.printStackTrace();
        }

        return document.getElementsByTagName("user");
	}

    //Generates the userlist from the xml file

    /**
     * This is used when the server starts. It reads the XML file and then returns an arraylist containing user objects.
     * Which is then used to set the observableUserList
     *
     * @return an arraylist containg the users from the XML file
     */
    public static ArrayList<User> xmlToList(){
            DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder documentBuilder;
            Document document = null;
            NodeList nodeList;
            ArrayList<User> userlist = new ArrayList<User>();

            try {
                documentBuilder = documentBuilderFactory.newDocumentBuilder();
                document = documentBuilder.parse(userfile);
                document.getDocumentElement().normalize();

            } catch(NullPointerException ne){
                Alert alert = new Alert(Alert.AlertType.ERROR);
                alert.setTitle("Error");
                alert.setResizable(true);
                alert.getDialogPane().setPrefSize(320, 200);
                alert.setHeaderText("Can not find the file containing the userlist!");
                alert.setContentText("userlist.xml is supposed to be located in Server/Resources folder, with a root element <Users></Users>");

                alert.showAndWait();
                System.exit(1);
            } catch (ParserConfigurationException e) {
                e.printStackTrace();
            } catch (IOException ioe) {
                ioe.printStackTrace();
            } catch (SAXException sae) {
                sae.printStackTrace();
            }

            nodeList = document.getElementsByTagName("user");

            for (int i = 0; i < nodeList.getLength(); i++) {
                Node userNode = nodeList.item(i);
                Element element = (Element) userNode;
                String username = element.getElementsByTagName("username").item(0).getTextContent();
                String password = element.getElementsByTagName("password").item(0).getTextContent();
                int userId = Integer.parseInt(element.getAttribute("id"));
                User user = new User(userId, username, password, UserStatus.OFFLINE);
                userlist.add(user);
            }
            return userlist;


    }
    //writes a new user to the xml file

    /**
     * This is used to write to the XML file when a new user is created
     * @param userId The userID that the user is to have
     * @param username The username that was chosen
     * @param password The password that was chosen
     */
    public static void writeToXml(int userId, String username, String password)
    {

        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder;
        Document document = null;
        NodeList nodeList;
        Element rootElement = null;


        try {
            documentBuilder = documentBuilderFactory.newDocumentBuilder();
            document = documentBuilder.parse(userfile);
            document.getDocumentElement().normalize();
            rootElement = document.getDocumentElement();

        }
        catch (ParserConfigurationException e) {
            e.printStackTrace();
        }
        catch (IOException ioe) {
            ioe.printStackTrace();
        }
        catch (SAXException sae) {
            sae.printStackTrace();
        }

        Element newUser = document.createElement("user");
        Element xmlUsername = document.createElement("username");
        Element xmlPassword = document.createElement("password");


        newUser.setAttribute("id",Integer.toString(userId));
        xmlUsername.appendChild(document.createTextNode(username));
        xmlPassword.appendChild(document.createTextNode(password));


        newUser.appendChild(xmlUsername);
        newUser.appendChild(xmlPassword);
        rootElement.appendChild(newUser);


        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        try {
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource domSource = new DOMSource(document);
            StreamResult streamResult = new StreamResult(userfile);
            transformer.transform(domSource, streamResult);

            DOMSource source = new DOMSource(document);
        } catch (TransformerConfigurationException e) {
            e.printStackTrace();
        } catch (TransformerException e) {
            e.printStackTrace();
        }

    }
    //Checks if username already exists in xml file

    /**
     *  Checks if the username is already taken in the XML file
     * @param username the username to check
     * @return true or false depending on whether the username is taken or not
     */
    public static boolean checkUsername(String username) {

            NodeList nodeList = getUserNodeList();
            for (int i = 0; i < nodeList.getLength(); i++) {
                Node userNode = nodeList.item(i);
                Element element = (Element) userNode;

                if (username.equals(element.getElementsByTagName("username").item(0).getTextContent())) {
                    return false;
                }
            }

            return true;
    }
}