用JAXB读取XML文件

Question

I can currently read the xml file:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer id="100" r="q">
<datas>
    <data>
        <age>29</age>
        <name>mky</name>
    </data>
</datas>
</customer>

Using the Customer class:

@XmlRootElement
public class Customer {

String name;
String age;
String id;
String r;

@XmlAttribute
public void setR(String R) {
    this.r = R;
}   

    /etc
}

I decided to extend the XML file to support multiple customers:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customers>
<customer id="100" r="q">
        <age>29</age>
        <name>mky</name>
</customer>
<customer id="101" r="q">
        <age>29</age>
        <name>mky</name>
</customer>
</customers>

I then ran into some trouble trying to read this.

I tried adding a Customers class:

@XmlRootElement
public class Customers{
private ArrayList<Customer> customers;

public List<Customer> getCustomers() {
    return customers;
}

@XmlElement
public void setCustomers(ArrayList<Customer> customers) {
    this.customers = customers;
}

}

And then trying to print this with:

     try {

            File file = new File("/Users/s.xml");
            JAXBContext jaxbContext = JAXBContext.newInstance(Customers.class);

            Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
            Customers c = (Customers) jaxbUnmarshaller.unmarshal(file);

            System.out.println(c.getCustomers());

          } catch (JAXBException e) {
            e.printStackTrace();
          }

        }}

But I'm getting a null value for trying to print this. Can someone enlighten me on how I can read the second XML file?

Answer 1

Change your Customers class to

@XmlRootElement(name = "customers")
class Customers {
    private List<Customer> customers;

    public List<Customer> getCustomers() {
        return customers;
    }

    @XmlElement(name = "customer")
    public void setCustomers(List<Customer> customers) {
        this.customers = customers;
    }
}

What you don't want is a mismatch between the get/set methods for the XML element. If one is returning ArrayList , the other should accept an ArrayList argument. Similarly for List (which is just good practice).

Answer 2

If you have problems using annotations, it is possible to remove them and use an instance of JAXBElement instead. To do so:

1. First delete any annotation in your Customers class

    public class Customers{ private ArrayList<Customer> customers; public List<Customer> getCustomers() { return customers; } public void setCustomers(ArrayList<Customer> customers) { this.customers = customers; } } 

2. Second use an instance of JAXBElement in your parsing method

    try { File file = new File("/Users/s.xml"); JAXBContext jaxbContext = JAXBContext.newInstance(Customers.class); Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller(); JAXBElement<Customers> je1 = unmarshaller.unmarshal(file, Customers.class); Customers c = je1.getValue(); System.out.println(c.getCustomers()); } catch (JAXBException e) { e.printStackTrace(); } } 

However note that annotations are required when you want to override default behavior. You find a full example here .