Marshalling the Java objects (without @XmlRootElement) to JSON via Jettison

Question

I have done the marshalling of an JAXB object (Which contains @XmlRootElement) to JSON using Jettison. But I can not convert a simple java object which has no annotations like @XmlRootElement to JSON. I would like to know "Is it mandatory to have that @XmlRootElement to marshall an object to JSON?"

I am getting the following Exception when I try to marshall the java object to Json

com.sun.istack.SAXException2: unable to marshal type "simpleDetail" as an element because it is missing an @XmlRootElement annotation

What could be the issue?

Solution

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

The JAXB (JSR-222) specification does not cover JSON-binding. Instead of using a JAXB implementation with the Jettison library, you could use EclipseLink JAXB (MOXy) that offers native JSON-binding. Below is an example.

JAVA MODEL

Foo

import java.util.List;
import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class Foo {

    private List<Bar> mylist;

}

Bar

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class Bar {

    private int id;
    private String name;

}

jaxb.properties

To specify MOXy as your JAXB provider you need to include a file called jaxb.properties in the same package as your domain model with the following entry (see: http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html):

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

DEMO CODE

Demo

MOXy does not require the @XmlRootElement annotation, and you can use the JSON_INCLUDE_ROOT property to tell MOXy to ignore the presence of any @XmlRootElement annotations. When the root element is ignored you need to use an unmarshal method that takes a class parameter to specify the type you are unmarshalling.

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

public class Demo {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>(2);
        properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");
        properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, false);
        JAXBContext jc = JAXBContext.newInstance(new Class[] {Foo.class}, properties);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        StreamSource json = new StreamSource("src/forum15404528/input.json");
        Foo foo = unmarshaller.unmarshal(json, Foo.class).getValue();

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(foo, System.out);
    }

}

input.json/Output

We see that no root element is present in the input or output.

{
   "mylist" : [ {
      "id" : 104,
      "name" : "Only one found"
   } ]
}

ADDITIONAL INFORMATION

• http://blog.bdoughan.com/2011/08/json-binding-with-eclipselink-moxy.html
• http://blog.bdoughan.com/2012/05/moxy-as-your-jax-rs-json-provider.html