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EclipseLink/UserGuide/MOXy/Relationships/Collections and Maps
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Key API
Contents
Collections
In this post will examine the different options JAXB offers for representing collections in XML. We will look at the following annotations:
* @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.
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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.
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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 each item in the collection will be marshalled to an XML element.
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<customer>
<emailAddresses>janed@example.com</emailAddresses> <emailAddresses>jdoe@example.org</emailAddresses>
</customer>
@XmlElement
We can control the name of the XML element a collection item is marshalled to by using the @XmlElement annotation.
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import java.util.*; import javax.xml.bind.annotation.*;
@XmlRootElement @XmlAccessorType(XmlAccessType.FIELD) public class Customer {
@XmlElement(name="email-address") private List<String> emailAddresses;
}
The following is the corresponding XML output:
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<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:
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<customer>janed@example.com jdoe@example.org</customer>