Revision as of 13:49, 5 April 2011

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Key API

Collections

JAXB contains several annotations to represent collections in XML:

• @XmlElement
• @XmlElementWrapper
• @XmlList
• @XmlList and @XmlAttribute
• @XmlList and @XmlValue

Java Model

For this example we will use the following model. We will apply different JAXB annotations to observe the effect it has on the XML representation.

import java.util.*;
import javax.xml.bind.annotation.*;
 
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
    private List<String> emailAddresses;
 
    public Customer() {
        emailAddresses = new ArrayList<String>();
    }
 
    public List<String> getEmailAddresses() {
        return emailAddresses;
    }
 
    public void setEmailAddresses(List<String> emailAddresses) {
        this.emailAddresses = emailAddresses;
    }
 
}

Demo Code

The following code will be used to convert the Customer object to XML. We will examine the impact of changing the metadata on the XML representation.

 
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
 
public class Demo {
 
    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Customer.class);
 
        Customer customer = new Customer();
        customer.getEmailAddresses().add("janed@example.com");
        customer.getEmailAddresses().add("jdoe@example.org");
 
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(customer, System.out);
    }
}

Default

By default, JAXB marshalls each item in the collection to an XML element:

 
<customer>
    <emailAddresses>janed@example.com</emailAddresses>
    <emailAddresses>jdoe@example.org</emailAddresses>
</customer>

@XmlElement

Use the '@XmlElement to control the name of the XML element that a collection item is marshalled to:

 
import java.util.*;
import javax.xml.bind.annotation.*;
 
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
    @XmlElement(name="email-address")
    private List<String> emailAddresses;
 
}

This will produce the following XML:

 
<customer>
    <email-address>janed@example.com</email-address>
    <email-address>jdoe@example.org</email-address>
</customer>

@XmlElementWrapper

Sometimes we want to add a grouping element to organize our collection data. This is done using the @XmlElementWrapper annotation.

1 2 3 4 5 6 7 8 9 10 11 12

import java.util.*; import javax.xml.bind.annotation.*;

@XmlRootElement @XmlAccessorType(XmlAccessType.FIELD) public class Customer {

   @XmlElementWrapper(name="email-addresses")
   @XmlElement(name="email-address")
   private List<String> emailAddresses;

}

The following is the corresponding XML output:

1 2 3 4 5 6

<customer>

   <email-addresses>
       <email-address>janed@example.com</email-address>
       <email-address>jdoe@example.org</email-address>
   </email-addresses>

</customer>

@XmlList

We can also represent our collection data as space seperated text. This is done using the @XmlList annotation.

1 2 3 4 5 6 7 8 9 10 11

import java.util.*; import javax.xml.bind.annotation.*;

@XmlRootElement @XmlAccessorType(XmlAccessType.FIELD) public class Customer {

   @XmlList
   private List<String> emailAddresses;

}

The following is the corresponding XML output:

1 2 3 4

<customer>

   <emailAddresses>janed@example.com jdoe@example.org</emailAddresses>

</customer>

@XmlList and @XmlAttribute

Since @XmlList allows us to represent a collection in a single piece of text it is also compatible with an XML attribute.

1 2 3 4 5 6 7 8 9 10 11 12

import java.util.*; import javax.xml.bind.annotation.*;

@XmlRootElement @XmlAccessorType(XmlAccessType.FIELD) public class Customer {

   @XmlList
   @XmlAttribute
   private List<String> emailAddresses;

}

The following is the corresponding XML output:

1 2

<customer

   emailAddresses="janed@example.com jdoe@example.org"/>

@XmlList and @XmlValue

Since @XmlList allows us to represent a collection in a single piece of text it is also compatible with a single text node.

1 2 3 4 5 6 7 8 9 10 11 12

import java.util.*; import javax.xml.bind.annotation.*;

@XmlRootElement @XmlAccessorType(XmlAccessType.FIELD) public class Customer {

   @XmlList
   @XmlValue
   private List<String> emailAddresses;

}

The following is the corresponding XML output:

1

<customer>janed@example.com jdoe@example.org</customer>

Special Schema Types	Advanced XML Schema Concepts	Bidirectional Relationships
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