如何从xml创建对象的arrayList？

Question

我有一个xml文件，结构如下：

 <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>

我还有一个类Contact，具有name、surname、code 和city 的属性。我正在尝试从 .xml 文件创建对象数组列表 Contact。 我的解决方案是这样的：

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;
        }

问题是开始读取文件，但在输入文件后立即返回等于null的所有内容。

提前感谢大家！

Answer 1

您可以为此目的使用 JAXB 库。例如：

使用联系人列表创建根类：

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

以及代表联系人数据的类：

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

然后使用Unmarshaller 读取您的 .xml 文件，例如：

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());
        }
}