Converting Java Object to Json using Marshaller

Question

Its quite easy to convert a java object to XML by using Marshaller. But I need to convert a java object to JSON by using marshaller alone. I know its good to use gson or Xstream like things., but I need to do using Marshaller.How to achieve it?

Thanks in advance.

Solution

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

Below is how this can be done if you are using MOXy as your JAXB provider.

• http://blog.bdoughan.com/2011/08/json-binding-with-eclipselink-moxy.html

JAVA MODEL

Customer

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

@XmlRootElement(namespace="http://www.example.com")
@XmlType(namespace="http://www.example.com")
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {

    @XmlAttribute
    private int id;

    @XmlElement(namespace="http://www.example.com")
    private String firstName;

    @XmlElement(namespace="http://www.example.com", nillable=true)
    private String lastName;

    @XmlElement(namespace="http://www.example.com")
    private List<PhoneNumber> phoneNumbers = new ArrayList<PhoneNumber>();

}

PhoneNumber

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class PhoneNumber {

    @XmlAttribute
    private String type;

    @XmlValue
    private String number;

}

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

input.xml

<?xml version="1.0" encoding="UTF-8"?>
<ns0:customer xmlns:ns0="http://www.example.com" id="123">
   <ns0:firstName>Jane</ns0:firstName>
   <ns0:lastName xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
   <ns0:phoneNumbers type="work">555-1111</ns0:phoneNumbers>
</ns0:customer>

Demo

In the demo code below we will use the same JAXB metadata to convert an XML document to Java objects, and then convert those objects back to JSON. With MOXy you can specify JSON output by setting a property on the Marshaller.

import java.io.File;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.MarshallerProperties;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Customer.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum15357366/input.xml");
        Customer customer = (Customer) unmarshaller.unmarshal(xml)
                ;
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.setProperty(MarshallerProperties.MEDIA_TYPE, "application/json");
        marshaller.setProperty(MarshallerProperties.JSON_INCLUDE_ROOT, false);
        marshaller.marshal(customer, System.out);
    }

}

JSON Output

Below is the JSON output. Note how there are no indicators corresponding to namespaces or XML attributes. Also note the collection of size one was correctly represented as a JSON array (a problem with some other approaches).

{
   "id" : 123,
   "firstName" : "Jane",
   "lastName" : null,
   "phoneNumbers" : [ {
      "type" : "work",
      "value" : "555-1111"
   } ]
}