Flexible marshalling with JAXB - jpa-2.0

Question

I'm hoping to have a flexible way of marshalling objects. A verbose version for single objects and a less-verbose version for multiple object versions.
For example, consider my department model:
GET /locations/1:
<location id='1'>
<link rel="self" href="http://example.com/locations/1"/>
<link rel="parent" href="http://example.com/serviceareas/1"/>
<name>location 01</name>
<departments>
<department id='1'>
<link rel="self" href="http://example.com/departments/1"/>
<name>department 01</name>
</department>
<department id='2'>
<link rel="self" href="http://example.com/departments/2"/>
<name>department 02</name>
</department>
<department id='3'>
<link rel="self" href="http://example.com/departments/3"/>
<name>department 03</name>
</department>
</departments>
</location>
GET /department/1:
<department id='1'>
<link rel="self" href="http://example.com/departments/1"/>
<link rel="parent" href="http://example.com/locations/1"/>
<name>department 01</name>
<abbr>dept 01</abbr>
....
<specialty>critical care</specialty>
</department>
Is there a way to do this? Would I need to have separate entity objects? One that references the table for CRUD operations and another for lists?

Answer 1

Note: I'm the EclipseLink JAXB (MOXy) lead, and a member of the JAXB 2 (JSR-222) expert group.
Your question is tagged EclipseLink, if you are using EclipseLink JAXB (MOXy) you can take advantage of the external binding document to apply a second mapping to the Department class.
ContextResolver
In a JAX-RS environment you can leverage MOXy's external binding document through a ContextResolver:
import java.io.*;
import java.util.*;
import javax.ws.rs.Produces;
import javax.ws.rs.ext.*;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.JAXBContextFactory;
#Provider
#Produces({"application/xml", "application/json"})
public class DepartmentContextResolver implements ContextResolver<JAXBContext> {
private JAXBContext jc;
public DepartmentContextResolver() {
try {
Map<String, Object> props = new HashMap<String, Object>(1);
props.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, "example/bindings.xml");
jc = JAXBContext.newInstance(new Class[] {Department.class} , props);
} catch(JAXBException e) {
throw new RuntimeException(e);
}
}
public JAXBContext getContext(Class<?> clazz) {
if(Department.class == clazz) {
return jc;
}
return null;
}
}
For More Information
http://blog.bdoughan.com/2011/04/moxys-xml-metadata-in-jax-rs-service.html
http://blog.bdoughan.com/2010/08/creating-restful-web-service-part-35.html
External Binding Document
By default MOXy's external binding document is used to augment the annotated model, but if you set the xml-mapping-metadata-complete flag it will completely override the annotations allowing you to apply a completely different mapping:
<xml-bindings
xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
package-name="example"
xml-mapping-metadata-complete="true">
...
</xml-bindings>
For More Information
http://blog.bdoughan.com/2011/09/mapping-objects-to-multiple-xml-schemas.html
http://blog.bdoughan.com/2010/12/extending-jaxb-representing-annotations.html
UPDATE
This update is to address a number of questions you asked in one of your comments:
1 . Should/can each ContentResolver have its own binding file?
Yes each ContextResolver should have its own binding file. The main reason for introducing a new ContextResolver is to represent a secondary mapping.
2 . Can I have more than one for each ContentResolver (this would give me a number of renderings of the same class, creating a 'view' of sorts), perhaps specifying its location in the constructor?
For a single ContextResolver you can express the metadata across multiple binding files, but they will be combined into a single set of mappings. This means that a single ContentResolver cannot have multiple views of a single class. A separate ContextResolver is used to represent a secondary mapping.
3 . Where should the binding files reside?
I recommend loading the metadata file from the class path.
http://blog.bdoughan.com/2011/04/moxys-xml-metadata-in-jax-rs-service.html
4 . I can see how the ContentResolver could be easily specified in a Resource's GET method, but how would this be done if the object is embedded in another (JPA) object? In the embedded object's getter/setter?
Your JAX-RS implementation should pick up your ContextResolver because it is annotated with #Provider. The ContextResolver used for a class will depend on how you implement the getContext method:
public JAXBContext getContext(Class<?> clazz) {
if(Customer.class == clazz) {
return jc;
}
return null;
}

Answer 2

Here comes another idea. Could be a bad idea but somewhat easy.
class Department {
#XmlElement(required = true)
public Link getSelf() {
return self;
}
#XmlElement(required = false) // default
public Link getParent() {
if (verbose) {
return parent;
}
return null;
}
#XmlElement(required = false) // default
public String getSpecialty() {
if (verbose) {
return specialty;
}
return null;
}
#XmlTransient
private boolean verbose;
}