One domain model, multiple json views

Question

We have a set of domain classes which are serialized to json via jackson using jersey services. We are currently annotating the classes with JAXB (although we're not tied to that). This works fine. But we want to offer different serializations of the classes for different use cases.

• Web site
• Mobile apps
• Admin tool
• Public API

In each of these cases there are different fields which we may or may not want included in the json view. For example, the admin tool might need some parameters for setting permissions on data. The mobile client needs a different URL to a media stream than the website. The website has particular naming conventions it needs for fields.

What is the best practice for managing different mappings of json for different service endpoints in Jersey?

Thanks!

Answer 1

Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.

MOXy offers JSON-binding based on JAXB annotations as well as an external binding document that allows you to apply alternate mappings to a domain model. I will demonstrate below with an example.

Metadata as JAXB Annotations

Below is a simple Java model mapping with the standard JAXB annotations.

package forum10761762;

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {

    int id;

    @XmlElement(name="first-name")
    String firstName;

    @XmlElement(name="last-name")
    String lastName;

}

Alternate Metadata #1 (alternate1.xml)

Here we will use the XML mapping document to unmap a couple of fields by making them @XmlTransient.

<?xml version="1.0"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum10761762">
    <java-types>
        <java-type name="Customer">
            <java-attributes>
                <xml-transient java-attribute="id"/>
                <xml-transient java-attribute="firstName"/>
             </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

Alternate Metadata #2 (alternate2.xml)

Here we will map the Java model to a different JSON structure using MOXy's path based mapping extension.

<?xml version="1.0"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum10761762">
    <java-types>
        <java-type name="Customer">
            <java-attributes>
                <xml-element java-attribute="firstName" xml-path="personalInfo/firstName/text()"/>
                <xml-element java-attribute="lastName" xml-path="personalInfo/lastName/text()"/>
             </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

Demo Code

package forum10761762;

import java.util.*;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.JAXBContextProperties;

public class Demo {

    public static void main(String[] args) throws Exception {
        Customer customer = new Customer();
        customer.id = 123;
        customer.firstName = "Jane";
        customer.lastName = "Doe";

        Map<String, Object> properties = new HashMap<String, Object>();
        properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");
        properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, false);

        // Output #1
        JAXBContext jc1 = JAXBContext.newInstance(new Class[] {Customer.class}, properties);
        marshal(jc1, customer);

        // Output #2
        properties.put(JAXBContextProperties.OXM_METADATA_SOURCE, "forum10761762/alternate1.xml");
        JAXBContext jc2 = JAXBContext.newInstance(new Class[] {Customer.class}, properties);
        marshal (jc2, customer);

        // Output #2
        properties.put(JAXBContextProperties.OXM_METADATA_SOURCE, "forum10761762/alternate2.xml");
        JAXBContext jc3 = JAXBContext.newInstance(new Class[] {Customer.class}, properties);
        marshal(jc3, customer);
    }

    private static void marshal(JAXBContext jc, Object object) throws Exception {
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(object, System.out);
        System.out.println();
    }

}

Output

Below is the output from running the demo code. Note from the same object model 3 different JSON documents were produced.

{
   "id" : 123,
   "first-name" : "Jane",
   "last-name" : "Doe"
}
{
   "last-name" : "Doe"
}
{
   "id" : 123,
   "personalInfo" : {
      "firstName" : "Jane",
      "lastName" : "Doe"
   }
}

For More Information (from my blog)

• JSON Binding with EclipseLink MOXy - Twitter Example
• MOXy as Your JAX-RS JSON Provider - MOXyJsonProvider
• MOXy's XML Metadata in a JAX-RS Service
• Specifying EclipseLink MOXy as Your JAXB Provider