Question

Okay so I’m creating a users class which asks for input then stores it in an XML file using java. I figured out to create the original XML file I think but I’m have trouble figuring out how to add a new user with the attribute “id” of one more then the previous User entry.

Here is the code I have so far:

/*imports */

    public class CreateUser {   
        static Scanner input = new Scanner(System.in);

/* object names*/
    String name;
    String age;
    String bday;
    String gender;
    String location;
    String orientation;
    String relationship;
    String hobbies;
    String choice;
    String username;
    String password;

    public void makeUser(){

/*left out code to get user entries here 

seemed irrelevant/*

    /*checks for file if it doesn't exist then it creates it else it should append
 the user to the xml document with a id increase of one.
 The appending part I'm not sure how to do.*/
File f = new File("C:\\Users\\Steven\\Workspace\\twitter\\src\\users.xml");
            if(f.exists()) { 
                try {
                    /* need help here*/
                }
            }
            else{
                try{
                    DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
                    DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
                    Document users = docBuilder.newDocument();

                    Element user = users.createElement("user");
                    users.appendChild(user);

                    Attr attr = users.createAttribute("id");
                    attr.setValue("0");
                    user.setAttributeNode(attr);

                    Element dname = users.createElement("name");
                    dname.appendChild(users.createTextNode(name));
                    user.appendChild(dname);

                    Element dgender = users.createElement("gender");
                    dgender.appendChild(users.createTextNode(gender));
                    user.appendChild(dgender);

                    Element dlocation = users.createElement("location");
                    dlocation.appendChild(users.createTextNode(location);
                    user.appendChild(dlocation);

                    Element dorientation = users.createElement("orientation");
                    dorientation.appendChild(users.createTextNode(orientation));
                    user.appendChild(dorientation);

                    Element drelationship = users.createElement("relationship");
                    drelationship.appendChild(users.createTextNode(relationship));
                    drelationship.appendChild(drelationship);


                    Element dhobbies = users.createElement("hobbies");
                    dhobbies.appendChild(users.createTextNode(hobbies));
                    dhobbies.appendChild(dhobbies);

                    Element dchoice = users.createElement("choice");
                    dchoice.appendChild(users.createTextNode(choice));
                    dchoice.appendChild(dchoice);

                    Element dusername = users.createElement("username");
                    dusername.appendChild(users.createTextNode(username));
                    dusername.appendChild(dusername);

                    Element dpassword = users.createElement("password");
                    dpassword.appendChild(users.createTextNode(password));
                    dpassword.appendChild(dpassword);

                    Element dbday = users.createElement("birthday");
                    dbday.appendChild(users.createTextNode(bday));
                    dbday.appendChild(dbday);

                    Element dage = users.createElement("age");
                    dage.appendChild(users.createTextNode(age));
                    dage.appendChild(dage);

                    TransformerFactory transformerFactory = TransformerFactory.newInstance();
                    Transformer transformer = transformerFactory.newTransformer();
                    DOMSource source = new DOMSource(users);
                    StreamResult result = new StreamResult(new File("C:\\Users\\Steven\\Workspace\\twitter\\src\\users.xml"));

                    StreamResult test = new StreamResult(System.out);
                    transformer.transform(source, result);
                } catch (ParserConfigurationException pce) {
                    pce.printStackTrace();
                } catch (TransformerException tfe) {
                    tfe.printStackTrace();
                }
            }
        }

I know its a lot of code to look through and I don’t want an exact coded answer but maybe just how to append the user with the attribute value one more then the previous entry. Or a point in a the direction of a helpful website. Anything really I’ve been perplexed for a little and I feel like I should get something this simple. Thanks in advance for any help

Answer 1

In your first section(if block), I think you can open your file in append mode as below to add an user, assuming user node is not wrapped in another node.

 StreamResult result = new StreamResult(
    new FileWriter("C:\\Users\\Steven\\Workspace\\twitter\\src\\users.xml", true));

There are two changes in above statement:

1. Using FileWriter in place of File
2. Using a second parameter true, which open the file in append mode.

EDIT: To get the max existing ID, you need to read file and look for ID tag as below:

  File xmlFile = new File("C:\\Users\\Steven\\Workspace\\twitter\\src\\users.xml");
  DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
  DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
  Document doc = dBuilder.parse(xmlFile);
  doc.getDocumentElement().normalize();
  NodeList nList = doc.getElementsByTagName("userId");//use the id tag name
  int maxId = 0;
  for(Node node: nList){
      if(Integer.parseInt(node.getTextContent()) > maxId ){
        maxId = Integer.parseInt(node.getTextContent());
      }
  }
  int newId = maxId +1; //use this ID
  xmlFile.close();//close the file