Question

This is quite straight forward. What is the minimum required structure for a Java POJO to be marshalled as a JSON?

Can you marshall an object as a JSON if it has only getters/setters or are the field declarations mandatory?

Setter/Getter example:

class Circle{
 private float radius;
 private float pi;

 // setter and getters for those aboce;

 public float getArea(){
 // returns the computed area;
 }
}

So can such an object be marshalled as a JSON if the “area” field is not defined in the Foo class as a field? Or is it mandatory to explicitly declare all fields in your POJO?

Answer 1

Note: I’m the EclipseLink JAXB (MOXy) lead and a member of the JAXB 2 (JSR-222) expert group.

Circle

For MOXy the only annotation required would be @XmlElement on the area property as there is no setter corresponding to the getter. The @XmlElement is included in Java SE 6 and above:

package forum10028037;

import javax.xml.bind.annotation.XmlElement;

class Circle{

    private float radius;
    private float pi;

    public float getRadius() {
        return radius;
    }

    public void setRadius(float radius) {
        this.radius = radius;
    }

    public float getPi() {
        return pi;
    }

    public void setPi(float pi) {
        this.pi = pi;
    }

    @XmlElement
    public float getArea(){
        return pi * radius * radius;
    }

}

Demo

package forum10028037;

import javax.xml.bind.*;

public class Demo {

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

        Circle circle = new Circle();
        circle.setPi(3.14f);
        circle.setRadius(10.1f);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.setProperty("eclipselink.media-type", "application/json");
        marshaller.setProperty("eclipselink.json.include-root", false);
        marshaller.marshal(circle, System.out);
    }

}

Output

{
   "area" : 320.31143,
   "pi" : 3.14,
   "radius" : 10.1
}

For More Information

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