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Difference between revisions of "EclipseLink/Release/2.4.0/JAXB RI Extensions/ID Resolver"

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= Design Documentation: ID Resolver =
 
= Design Documentation: ID Resolver =
 
[http://bugs.eclipse.org/360249 ER 360249]
 
  
 
In the current JAXB RI, developed by Sun, there is a series of "proprietary" JAXB extensions which provide advanced functionality outside of the JAXB specification (these extension classes and properties reside in the '''com.sun.xml.bind''' package).
 
In the current JAXB RI, developed by Sun, there is a series of "proprietary" JAXB extensions which provide advanced functionality outside of the JAXB specification (these extension classes and properties reside in the '''com.sun.xml.bind''' package).

Revision as of 11:31, 18 June 2012

Design Documentation: ID Resolver

In the current JAXB RI, developed by Sun, there is a series of "proprietary" JAXB extensions which provide advanced functionality outside of the JAXB specification (these extension classes and properties reside in the com.sun.xml.bind package).

The abstract class IDResolver provided in the Sun JAXB implementation allows users to override the ID/IDREF processing of the JAXB runtime.

This document will outline the design for an EclipseLink equivalent to this extension.


Behaviour

If an IDResolver has been set on the Unmarshaller (via properties), then the following things must happen during unmarshal:

  • The IDResolver's startDocument() method must be called when unmarshalling starts.
  • When an ID value is encountered during unmarshal, the IDResolver's bind method must be called, to bind the object to the ID.
  • When an IDREF value is encountered during unmarshal, the IDResolver's resolve method must be used to obtain the object for the IDREF.
  • The IDResolver's endDocument() method must be called when unmarshalling completes.


Configuration

The user must extend the org.eclipse.persistence.jaxb.IDResolver class and implement the following abstract methods (startDocument and endDocument are optional):

public abstract Callable<?> resolve(Object id, Class type) throws SAXException;
 
public abstract Callable<?> resolve(Map<String, Object> id, final Class type) throws SAXException;
 
public abstract void bind(Object id, Object obj) throws SAXException;
 
public abstract void bind(Map<String, Object> id, Object obj) throws SAXException;
 
public void startDocument(ValidationEventHandler errorHandler) throws SAXException {}
 
public void endDocument() throws SAXException {}

The user's IDResolver class can then be passed to the Unmarshaller through the setProperty() method:

...
JAXBContext ctx = ...
Unmarshaller u = ctx.createUnmarshaller();
u.setProperty(UnmarshallerProperties.ID_RESOLVER, new MyIDResolver());
...

Note: EclipseLink also supports Sun's IDResolver property names:

m.setProperty("com.sun.xml.bind.IDResolver", new MyResolver());
m.setProperty("com.sun.xml.internal.bind.IDResolver", new MyResolver());

Also note that if you are using a Sun IDResolver with EclipseLink, it will be unable to support EclipseLink's multiple XML IDs feature. In this case, you should re-implement your IDResolver as a subclass of org.eclipse.persistence.jaxb.IDResolver.


Appendix A - Example IDResolver

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.Callable;
 
import javax.xml.bind.ValidationEventHandler;
 
import org.eclipse.persistence.jaxb.IDResolver;
 
import org.xml.sax.SAXException;
 
public class MyIDResolver extends IDResolver {
   Map<Map<String, Object>, Apple> apples = new LinkedHashMap();
   Map<Map<String, Object>, Orange> oranges = new LinkedHashMap();
 
   @Override
   public void startDocument(ValidationEventHandler eventHandler) throws SAXException {
       apples.clear();
       oranges.clear();
   }
 
   @Override
   public void endDocument() throws SAXException {
   }
 
   @Override
   public void bind(Map<String, Object> idWrapper, Object obj) throws SAXException {
       if (obj instanceof Apple) {
           ((Apple) obj).processed = true;
           apples.put(idWrapper, (Apple) obj);
       } else {
           ((Orange) obj).processed = true;
           oranges.put(idWrapper, (Orange) obj);
       }
   }
 
   @Override
   public Callable<Object> resolve(final Map<String, Object> idWrapper, final Class type) throws SAXException {
       return new Callable<Object>() {
           public Object call() {
               if (type == Apple.class) {
                   return apples.get(idWrapper);
               } else {
                   return oranges.get(idWrapper);
               }
           }
       };
   }
 
   @Override
   public void bind(Object id, Object obj) throws SAXException {
       Map<String, Object> idMap = new LinkedHashMap<String, Object>(1);
       idMap.put("stringId", id);
       bind(idMap, obj);
   }
 
   @Override
   public Callable<?> resolve(Object id, Class type) throws SAXException {
       Map<String, Object> idMap = new LinkedHashMap<String, Object>(1);
       idMap.put("stringId", id);
       return resolve(idMap, type);
   }
 
}