How to create an arrayList of objects from xml?

Question

I have an xml file, with the following structure:

 <elements number="3">
     <contact>
       <name>PAUL</name>
       <surname>ONE</surname>
       <code>A1</code>
       <city>NEWYORK</city>
     </contact>
     <contact>
       <name>LAURA</name>
       <surname>TWO</surname>
       <code>A2</code>
       <city>WASHINGTON</city>
     </contact>
     <contact>
       <name>JOHN</name>
       <surname>THREE</surname>
       <code>A3</code>
       <city>BOSTON</city>
     </contact>

I also have a class Contact, with the attributes name, surname, code and city. I am trying to create an arrayList of objects Contact from the .xml file. My solution would be so:

private String inputContacts ="inputContacts.xml";

public ArrayList<Contact> readContacts() {
        ArrayList<Contact> contacts = new ArrayList<Contact>();
        int k = 0;
        try {
            xmlif = XMLInputFactory.newInstance();
            xmlr = xmlif.createXMLStreamReader(inputContacts, new FileInputStream(inputContacts)); 

            while (xmlr.hasNext()) {
                 switch (xmlr.getEventType()) {
                 case XMLStreamConstants.START_DOCUMENT: 
                     System.out.println("Start Read Doc " + inputContacts); 
                     break;

                 case XMLStreamConstants.START_ELEMENT: 
                    switch (xmlr.getLocalName()) {
                    case "contact":
                         System.out.println("Tag " + xmlr.getLocalName());
                         Contact p = new Contact();
                         contacts.add(p);
                         k++;
                        break;

                    case "name":
                        contacts.get(k).setName(xmlr.getText());
                        break;

                    case "surname":
                        contacts.get(k).setSurname(xmlr.getText());
                        break;

                    case "code":
                        contacts.get(k).setCode(xmlr.getText());
                        break;

                    case "city":
                        contacts.get(k).setCity(xmlr.getText());
                        break;

                    default:
                        break; 
                     }

                     break;
                 case XMLStreamConstants.END_ELEMENT: 
                     System.out.println("END-Tag " + xmlr.getLocalName()); 

                     break;
                 case XMLStreamConstants.COMMENT:
                    System.out.println("// comment " + xmlr.getText()); 
                     break;
                 case XMLStreamConstants.CHARACTERS: 

                     break;

                 }

                xmlr.next();
            }
        }
        catch (Exception e) {
            System.out.println("Reader initialization error:");
            System.out.println(e.getMessage()); 
            }

        return contacts;
        }

The problem is that is starts reading the file, but immediately after having entered in the document, it return everything equals to null.

Thanks in advance to everybody!

You set k=0 in the beginning, and then increment it after adding a new element, and then try to address this element by k, which is equal to 1 at this point. But arrays are indexed from 0, so you should get IndexOutOfBoundsException. Try to set k=-1 initially. — Egor
– Egor, Commented Apr 28, 2019 at 13:24

Piotr S · Accepted Answer · 2019-04-28 13:16:50Z

1

You can use JAXB library for this purpose. For example:

Create root class with list of contacts:

@XmlRootElement(name = "elements")
@XmlAccessorType(XmlAccessType.FIELD)
public class ContactsList {
    @XmlElement(name = "contact")
    private List<Contact> list;
}

and class which represents Contact data:

@XmlRootElement(name = "contact")
public class Contact {
    private String name;
    private String surname;   
    private String code;   
    private String city;
}

and then using Unmarshaller read your .xml file e.g.:

public static void main(String[] args) throws JAXBException {
        File file = new File("your-file.xml");
        JAXBContext jaxbContext = JAXBContext.newInstance(ContactsList.class);
        Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
        ContactsList contacts = (ContactsList) unmarshaller.unmarshal(file);
        for (Contact c: contacts.getList()) {
            System.out.println(c.toString());
        }
}

answered Apr 28, 2019 at 13:16

Piotr S

1373 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

devOn Over a year ago

Isn’t there a way without external libraries, but the one I already included?

Collectives™ on Stack Overflow

How to create an arrayList of objects from xml?

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related