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Developing JAXB Applications Using EclipseLink MOXy, Release 2.4
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Using Virtual Access Methods

In addition to standard JAXB properties (represented by Java fields and accessor methods), EclipseLink MOXy 2.3 introduced the concept of virtual properties and virtual access methods, which instead rely on special get() and set() methods to maintain mapping data. For example, you might want to use a HashMap as the underlying structure to hold data for certain mappings. The mappings that use virtual method access must be defined in EclipseLink OXM metadata.

In order to add virtual properties to an entity:


NoteNote:

By default, EclipseLink will look for methods named set and get. To customize accessor method names, see "Specifying Alternate Accessor Methods".


For an example of using virtual properties in a multi-tenant architecture, see "Using Extensible MOXy".

Configuring Virtual Access Methods

Virtual Access Methods can be configured either by through Java annotations (see Example 8-5) or EclipseLink OXM metadata (see Example 8-6).

Example 8-5 Using Java Annotations

package example;
 
import java.util.Map;
import java.util.HashMap;
 
import javax.xml.bind.annotation.*;
 
import org.eclipse.persistence.oxm.annotations.XmlVirtualAccessMethods;
 
@XmlRootElement
@XmlVirtualAccessMethods
@XmlAccessorType(XmlAccessType.PROPERTY)
public class Customer {
 
   private int id;
 
   private String name;
 
   private Map<String, Object> extensions = new HashMap<String, Object>();
 
   public Object get(String name) {
      return extensions.get(name);
   }
 
   public void set(String name, Object value) {
      extensions.put(name, value);
   }
 
   @XmlAttribute
   public int getId() {
   ...
 
}
 

Example 8-6 Using OXM Metadata

...
<java-types>
   <java-type name="Customer">
      <xml-virtual-access-methods />
      <java-attributes>
         <xml-attribute java-attribute="id" />
         <xml-element java-attribute="name" />
      </java-attributes>
   </java-type>
...
 

Example

For this example we will use the Customer class (Example 8-3), along with an EclipseLink OXM file to define our virtual mappings. Any property encountered in this file that does not have a corresponding Java attribute will be considered a virtual property and will be accessed through the virtual access methods. Because there is no associated Java field, the type information must also be provided.

Example 8-7 The virtualprops-oxm.xml File

...
<java-types>
    <java-type name="Customer">
        <java-attributes>
            <xml-element java-attribute="discountCode" name="discount-code"
                type="java.lang.String" />
        </java-attributes>
    </java-type>
</java-types>
...
 

When creating the JAXBContext, we pass in the virtualprops metadata along with our Customer class.

To set the values for virtual properties, we will use the aforementioned set() method.

InputStream oxm = classLoader.getResourceAsStream("virtualprops-oxm.xml");
Map<String, Object> properties = new HashMap<String, Object>();
properties.put(JAXBContextProperties.OXM_METADATA_SOURCE, oxm);
 
Class[] classes = new Class[] { Customer.class };
JAXBContext ctx = JAXBContext.newInstance(classes, properties);
 
Customer c = new Customer();
c.setId(7761);
c.setName("Bob Smith");
c.set("discountCode", "SIUB372JS7G2IUDS7");
 
ctx.createMarshaller().marshal(e, System.out);
 

This will produce the following XML:

<customer id="7761">
   <name>Bob Smith</name>
   <discount-code>SIUB372JS7G2IUDS7</discount-code>
</customer>
 

Conversely, we use the get(String) method to access virtual properties:

...
Customer c = (Customer) ctx.createUnmarshaller().unmarshal(CUSTOMER_URL);
 
// Populate UI
customerWindow.getTextField(ID).setText(String.valueOf(c.getId()));
customerWindow.getTextField(NAME).setText(c.getName());
customerWindow.getTextField(DCODE).setText(c.get("discountCode"));
...
 

Using XmlAccessType.FIELD and XmlTransient

If you are using an @XmlAccessorType of XmlAccessType.FIELD, you will need to mark your virtual properties Map attribute to be @XmlTransient, to prevent the Map itself from being bound to XML:

Example 8-8 Marking the Map Attribute

package example;
 
import javax.xml.bind.annotation.*;
 
import org.eclipse.persistence.oxm.annotations.XmlVirtualAccessMethods;
 
@XmlRootElement
@XmlVirtualAccessMethods
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
   @XmlTransient
   private Map<String, Object> extensions;
   ...
 

Options

Specifying Alternate Accessor Methods

To use different method names as your virtual method accessors, specify them using the getMethodName and setMethodName attributes on @XmlVirtualAccessMethods:

Example 8-9 Using Alternate Accessor Methods

package example;
 
import java.util.Properties;
 
import javax.xml.bind.annotation.*;
 
import org.eclipse.persistence.oxm.annotations.XmlVirtualAccessMethods;
 
@XmlRootElement
@XmlVirtualAccessMethods(getMethod = "getCustomProps", setMethod = "putCustomProps")
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
   @XmlAttribute
   private int id;
 
   private String name;
 
   @XmlTransient
   private Properties<String, Object> props = new Properties<String, Object>();
 
   public Object getCustomProps(String name) {
      return props.getProperty(name);
   }
 
   public void putCustomProps(String name, Object value) {
      props.setProperty(name, value);
   }
 
}
 

In OXM:

Example 8-10 Using the xml-virtual-access-methods Element

...
<java-types>
  <java-type name="Customer">
    <xml-virtual-access-methods get-method="getCustomProps" set-method="putCustomProps" />
    <java-attributes>
      <xml-attribute java-attribute="id" />
      <xml-element java-attribute="name" />
      <!-- virtual -->
      <xml-element java-attribute="discountCode" name="discount-code"
        type="java.lang.String" />
    </java-attributes>
  </java-type>
...
 

Specifying Schema Generation Options

You can configure how virtual properties should appear in generated schemas using the schema attribute on @XmlVirtualAccessMethods. EclipseLink offers two options. Virtual properties can be:

  • written as individual nodes, or

  • consolidated into a single <any> element.

Virtual Properties as Individual Nodes

This is EclipseLink's default behavior, or can be specified explicitly as an override as follows:

Example 8-11 Mapping as Individual Nodes

package example;
 
@XmlRootElement
@XmlVirtualAccessMethods(schema = XmlVirtualAccessMethodsSchema.NODES)
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
   ...
 

For example:

Example 8-12 Original Customer Schema

<xs:schema ...>
 
    <xs:element name="customer">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="first-name" type="xs:string" />
                <xs:element name="last-name" type="xs:string" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>
 
</xs:schema>
 

Example 8-13 Generated Schema (After adding middle-initial and phone-number)

<xs:schema ...>
 
    <xs:element name="customer">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="first-name" type="xs:string" />
                <xs:element name="last-name" type="xs:string" />
                <xs:element name="middle-initial" type="xs:string" />
                <xs:element name="phone-number" type="xs:string" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>
 
</xs:schema>
 

Virtual Properties in an <any> Element

EclipseLink can also use an <any> element to hold all of the virtual properties in one node:

Example 8-14 Using an <any> Element

package example;
 
@XmlRootElement
@XmlVirtualAccessMethods(schema = XmlVirtualAccessMethodsSchema.ANY)
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
   ...
 

From Example 8-14, a newly generated schema using this approach would look like:

Example 8-15 Generated Schema

<xs:schema ...>
 
    <xs:element name="customer">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="first-name" type="xs:string" />
                <xs:element name="last-name" type="xs:string" />
                <xs:any minOccurs="0" />
            </xs:sequence>
        </xs:complexType>
   </xs:element>
 
</xs:schema>
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