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EclipseLink/UserGuide/MOXy/Relationships/Collections and Maps
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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.
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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:
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<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.
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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:
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<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.
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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:
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<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.
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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>