Revision as of 11:02, 21 June 2011

EclipseLink
Website
Download
Community
Mailing List • Forums • IRC • mattermost
Issues
Open • Help Wanted • Bug Day
Contribute
Browse Source

Key API

• XmlVirtualAccessMethods

Virtual Access Methods

In addition to the standard JAXB access methods (public member, field, property, etc.), EclipseLink MOXy 2.3 introduces the concept of "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:

• the Java class must be marked with an @XmlVirtualAccessMethods annotation, or <xml-virtual-access-methods> element in OXM
• the Java class must contain getter and setter methods to access virtual property values
  • public Object get(String propertyName)
  • public void set(String propertyName, Object value)
  • method names are configurable but must have the same method signatures as above

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

Example

For this example we will use the following Employee class. In addition to some conventional JAXB mappings, we also specify that this class contains virtual access methods by including the @XmlVirtualAccessMethods annotation.

Using Annotations

@XmlRootElement
@XmlVirtualAccessMethods
@XmlAccessorType(AccessType.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() {
   ...
 
}

Using EclipseLink OXM

@XmlVirtualAccessMethods can be specified in OXM as follows:

Next, we define our virtual mappings in an EclipseLink OXM file. 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.

XmlAccessorType and XmlTransient

If you are using an @XmlAccessorType other than AccessType.PROPERTY, you will need to mark your virtual properties Map attribute to be @XmlTransient, to prevent the Map itself from being bound to XML.

@XmlRootElement
@XmlVirtualAccessMethods
@XmlAccessorType(AccessType.FIELD)
public class Customer {
 
   @XmlTransient
   private Map<String, Object> extensions;
   ...