Revision as of 16:33, 6 July 2011

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Key API

• MetadataSource
• MetadataSourceAdapter
• XMLMetadataSource
• XmlBindings

XML MetadataSource

EclipseLink 2.3 introduces the concept of a MetadataSource, which is responsible for serving up EclipseLink metadata. This allows you to store mapping information outside of your application and have it retrieved when the application's JAXBContext is being created or refreshed.

Implementing a MetadataSource

To implement your own MetadataSource, you can:

• Create a new class that implements the org.eclipse.persistence.jaxb.metadata.MetadataSource interface.
• Create a new class that extends the org.eclipse.persistence.jaxb.metadata.MetadataSourceAdapter class. Using this method is preferred, as it will insulate you from future additions to the interface.

In either case, you will be responsible for implementing the following method:

/**
 * Retrieve XmlBindings according to the JAXBContext bootstrapping information.
 *
 * @param properties - The properties passed in to create the JAXBContext
 * @param classLoader - The ClassLoader passed in to create the JAXBContext
 * @return the XmlBindings object representing the metadata
 */
XmlBindings getXmlBindings(Map<String, ?> properties, ClassLoader classLoader);

XmlBindings

Internally, EclipseLink metadata is stored in an XmlBindings object tree, which itself is mapped with JAXB. This means that you can actually use a JAXBUnmarshaller to read external metadata and create an XmlBindings from it:

...
 
JAXBContext xmlBindingsContext = JAXBContext.newInstance("org.eclipse.persistence.jaxb.xmlmodel");
FileReader bindingsFile = new FileReader("eclipselink-oxm.xml");
XmlBindings bindings = (XmlBindings) xmlBindingsContext.createUnmarshaller().unmarshal(bindingsFile);
 
...

Example

The following example retrieves metadata XML from a URL, and then creates an XmlBindings object by unmarshalling

Specifying the MetadataSource

To use a MetadataSource in creating a JAXBContext, add it to the properties map with the key JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY:

MetadataSource metadataSource = new MyMetadataSourceImpl();
 
Map<String, Object> properties = new HashMap<String, Object>(1);
properties.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, metadataSource);
 
JAXBContext jc = JAXBContext.newInstance(new Class[] { Customer.class }, properties);