Using JAXB to Implement a Copy Operation

The following post was inspired by an answer I gave to a question on Stack Overflow (feel free to up vote).  I am not suggesting that JAXB should be used to implement copy methods, instead I'm using a copy operation to demonstrate that JAXB can treat an object model as XML input.  


Java Model

The following domain model will be used for this example.  The only annotation I have used is @XmlRootElement.  Below I will describe how the copy operation can be performed with or without this annotation.

package blog.copy;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Customer {

    private String name;
    private Address address;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

}

and

package blog.copy;

public class Address {

    private String street;
    private String city;

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

}

Demo Code - With @XmlRootElement


When the root object is annotated with @XmlRootElement the copy operation involves the following steps:

1. Wrap the object to be copied in a JAXBSource
2. Unmarshal the JAXBSource

package blog.copy;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.util.JAXBSource;

public class Demo {

    public static void main(String[] args) throws Exception {
        // Build an instance of Customer with an Address
        Customer originalCustomer = new Customer();
        originalCustomer.setName("Jane Doe");
        Address originalAddress = new Address();
        originalAddress.setStreet("123 A Street");
        originalAddress.setCity("Any Town");
        originalCustomer.setAddress(originalAddress);

        // Create the JAXBContext
        JAXBContext jc = JAXBContext.newInstance(Customer.class);

        // Wrap the Customer object in a JAXBSource
        JAXBSource source = new JAXBSource(jc, originalCustomer);

        // Treat the JAXBSource as an XML input and unmarshal it
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        Customer copiedCustomer = (Customer) unmarshaller.unmarshal(source);

        // Marshal the copy of Customer to demonstrate that it is populated
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(copiedCustomer, System.out);
    }

}

Demo Code - Without @XmlRootElement

When the root object is not annotated with @XmlRootElement the copy operation is slightly longer:

1. Wrap the object to be marshalled in a JAXBElement
2. Wrap the JAXBElement in a JAXBSource
3. Unmarshal the JAXBSource passing the target class as a parameter

package blog.copy;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.util.JAXBSource;
import javax.xml.namespace.QName;

public class JAXBElementDemo {

    public static void main(String[] args) throws Exception {
        // Build an instance of Customer with an Address
        Customer originalCustomer = new Customer();
        originalCustomer.setName("Jane Doe");
        Address originalAddress = new Address();
        originalAddress.setStreet("123 A Street");
        originalAddress.setCity("Any Town");
        originalCustomer.setAddress(originalAddress);

        // Create the JAXBContext
        JAXBContext jc = JAXBContext.newInstance(Customer.class);

        // Wrap the Customer object in a JAXBElement and a JAXBSource
        JAXBElement<Customer> originalJAXBElement = 
            new JAXBElement<Customer>(new QName("root"),Customer.class, originalCustomer);
        JAXBSource source = new JAXBSource(jc, originalJAXBElement);

        // Treat the JAXBSource as an XML input and unmarshal it
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        JAXBElement<Customer> copiedJAXBElement = unmarshaller.unmarshal(source, Customer.class);
        Customer copiedCustomer = copiedJAXBElement.getValue();

        // Marshal the copy of Customer to demonstrate that it is populated
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(copiedJAXBElement, System.out);
    }

}

Further Reading


If you found this post useful, then you may also be interested in:

• Validate a JAXB Object Model With an XML Schema