Using MetadataSource

The MetadataSource, introduced in EclipseLink 2.3, 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:

Example 2-20 Implementing the XMlBindings 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);

Using an XmlBindings Object

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

Example 2-21 Sample XmlBindings Object

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

Specifying the MetadataSource

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

Example 2-22 Adding MetadataSource to the Properties Map

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

MetadataSource Example

The following example creates an XmlBindings object by unmarshalling from a URL:

Example 2-23 Sample XmlBindings Object

package example;
 
import java.net.URL;
import java.util.Map;
 
import javax.xml.bind.JAXBContext;
 
import org.eclipse.persistence.jaxb.metadata.MetadataSourceAdapter;
import org.eclipse.persistence.jaxb.xmlmodel.XmlBindings;
 
public class MyMetadataSource extends MetadataSourceAdapter {
 
   private JAXBContext bindingsContext;
   private URL bindingsUrl;
 
   private final String XML_BINDINGS_PACKAGE = "org.eclipse.persistence.jaxb.xmlmodel";
   private final String METADATA_URL = "http://www.example.com/private/metadata/xml-bindings.xml"; 
   public MyMetadataSource() {
      try {
         bindingsContext = JAXBContext.newInstance(XML_BINDINGS_PACKAGE);
         bindingsUrl = new URL(METADATA_URL);
      } catch (Exception e) {
         throw new RuntimeException(e);
      }
   }
 
   @Override
   public XmlBindings getXmlBindings(Map<String, ?> properties, ClassLoader classLoader) {
      try {
         Unmarshaller u = bindingsContext.createUnmarshaller();
         XmlBindings bindings = (XmlBindings) u.unmarshal(bindingsUrl);
         return bindings;
      } catch (Exception e) {
         throw new RuntimeException(e);
      }
   }
 
}

Building XmlBindings Programatically

You also have the option of building your own XmlBindings object from scratch in code. The example below modifies the pCode field of the Address class to use a locale-specific name:

Example 2-24 Sample XmlBindings Object

package example;
 
import java.util.Locale;
import java.util.Map;
 
import org.eclipse.persistence.jaxb.metadata.MetadataSourceAdapter;
import org.eclipse.persistence.jaxb.xmlmodel.JavaType;
import org.eclipse.persistence.jaxb.xmlmodel.JavaType.JavaAttributes;
import org.eclipse.persistence.jaxb.xmlmodel.ObjectFactory;
import org.eclipse.persistence.jaxb.xmlmodel.XmlBindings;
import org.eclipse.persistence.jaxb.xmlmodel.XmlBindings.JavaTypes;
import org.eclipse.persistence.jaxb.xmlmodel.XmlElement;
 
public class AddressMetadataSource extends MetadataSourceAdapter {
 
    private ObjectFactory factory;
    private XmlBindings xmlBindings;
 
    public AddressMetadataSource() {
        factory = new ObjectFactory();
 
        xmlBindings = new XmlBindings();
        xmlBindings.setPackageName("example");
        xmlBindings.setJavaTypes(new JavaTypes());
    }
 
    @Override
    public XmlBindings getXmlBindings(Map<String, ?> properties, ClassLoader classLoader) {
        JavaType javaType = new JavaType();
        javaType.setName("Address");
        javaType.setJavaAttributes(new JavaAttributes());
 
        XmlElement pCodeElement = new XmlElement();
        pCodeElement.setJavaAttribute("pCode");
 
        String country = Locale.getDefault().getCountry(); 
        if (country.equals(Locale.US.getCountry())) {
            pCodeElement.setName("zip-code");
        } else if (country.equals(Locale.UK.getCountry())) {
            pCodeElement.setName("post-code");
        } else if (country.equals(Locale.CANADA.getCountry())) {
            pCodeElement.setName("postal-code");
        }
 
        javaType.getJavaAttributes().getJavaAttribute().add(factory.createXmlElement(pCodeElement));
 
        xmlBindings.getJavaTypes().getJavaType().add(javaType);
        return xmlBindings;
    }
 
}