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Difference between revisions of "EclipseLink/UserGuide/MOXy/Relationships/Collections and Maps"

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'''Example'''
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{{EclipseLink_UserGuide
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*http://bdoughan.blogspot.com/2010/09/jaxb-collection-properties.html
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|info=y
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|toc=y
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|eclipselink=y
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|eclipselinktype=MOXy
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|api=y
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|apis= *
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}}
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=Collections =
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In this post will examine the different options JAXB offers for representing collections in XML.  We will look at the following annotations:
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    * @XmlElement
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    * @XmlElementWrapper
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    * @XmlList
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    * @XmlList and @XmlAttribute
 +
    * @XmlList and @XmlValue
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 +
 
 +
Java Model
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 +
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.*;
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import javax.xml.bind.annotation.*;
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@XmlRootElement
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@XmlAccessorType(XmlAccessType.FIELD)
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public class Customer {
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    private List<String> emailAddresses;
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    public Customer() {
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        emailAddresses = new ArrayList<String>();
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    }
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    public List<String> getEmailAddresses() {
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        return emailAddresses;
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    }
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    public void setEmailAddresses(List<String> emailAddresses) {
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        this.emailAddresses = emailAddresses;
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    }
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}
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Demo Code
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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;
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import javax.xml.bind.Marshaller;
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public class Demo {
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    public static void main(String[] args) throws Exception {
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        JAXBContext jc = JAXBContext.newInstance(Customer.class);
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        Customer customer = new Customer();
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        customer.getEmailAddresses().add("janed@example.com");
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        customer.getEmailAddresses().add("jdoe@example.org");
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        Marshaller marshaller = jc.createMarshaller();
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        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
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        marshaller.marshal(customer, System.out);
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    }
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}
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Default
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By default each item in the collection will be marshalled to an XML element.
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<customer>
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    <emailAddresses>janed@example.com</emailAddresses>
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    <emailAddresses>jdoe@example.org</emailAddresses>
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</customer>
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@XmlElement
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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.*;
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import javax.xml.bind.annotation.*;
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@XmlRootElement
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@XmlAccessorType(XmlAccessType.FIELD)
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public class Customer {
 +
 +
    @XmlElement(name="email-address")
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    private List<String> emailAddresses;
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}
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The following is the corresponding XML output:
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<customer>
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    <email-address>janed@example.com</email-address>
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    <email-address>jdoe@example.org</email-address>
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</customer>
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@XmlElementWrapper
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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.*;
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import javax.xml.bind.annotation.*;
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@XmlRootElement
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@XmlAccessorType(XmlAccessType.FIELD)
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public class Customer {
 +
 +
    @XmlElementWrapper(name="email-addresses")
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    @XmlElement(name="email-address")
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    private List<String> emailAddresses;
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}
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The following is the corresponding XML output:
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<customer>
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    <email-addresses>
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        <email-address>janed@example.com</email-address>
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        <email-address>jdoe@example.org</email-address>
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    </email-addresses>
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</customer>
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@XmlList
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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.*;
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import javax.xml.bind.annotation.*;
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@XmlRootElement
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@XmlAccessorType(XmlAccessType.FIELD)
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public class Customer {
 +
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    @XmlList
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    private List<String> emailAddresses;
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}
 +
 
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The following is the corresponding XML output:
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<customer>
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    <emailAddresses>janed@example.com jdoe@example.org</emailAddresses>
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</customer>
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@XmlList and @XmlAttribute
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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.*;
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import javax.xml.bind.annotation.*;
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@XmlRootElement
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@XmlAccessorType(XmlAccessType.FIELD)
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public class Customer {
 +
 +
    @XmlList
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    @XmlAttribute
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    private List<String> emailAddresses;
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 +
}
 +
 
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The following is the corresponding XML output:
 +
 
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<customer
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    emailAddresses="janed@example.com jdoe@example.org"/>
 +
 
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@XmlList and @XmlValue
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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.*;
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import javax.xml.bind.annotation.*;
 +
 +
@XmlRootElement
 +
@XmlAccessorType(XmlAccessType.FIELD)
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public class Customer {
 +
 +
    @XmlList
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    @XmlValue
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    private List<String> emailAddresses;
 +
 +
}
 +
 
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The following is the corresponding XML output:
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<customer>janed@example.com jdoe@example.org</customer>
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{{EclipseLink_MOXy
 +
|previous= [[EclipseLink/UserGuide/MOXy/Simple_Values/Special_Schema_Types|Special Schema Types]]
 +
|up=    [[EclipseLink/UserGuide/MOXy/Advanced_XML_Schema_Concepts|Advanced XML Schema Concepts]]
 +
|next=      [[EclipseLink/UserGuide/MOXy/Relationships/Bidirectional_Relationships|Bidirectional Relationships]]
 +
|version=2.2.0 Draft
 +
}}

Revision as of 13:45, 5 April 2011

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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.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

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.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

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.

1 2 3 4

<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.

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 { 

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

}

The following is the corresponding XML output:

1 2 3 4

<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>


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Version: 2.2.0 Draft
Other versions...

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