Domain Model
By default a JAXB (JSR-222) implementation will not include a mapped field/property with a null value in the output. If you want the null value represented then you simply add the following annotation @XmlElement(nillable=true).
package blog.json.nillable;
import javax.xml.bind.annotation.*;
@XmlRootElement
public class Customer {
private String firstName;
private String middleName;
private String lastName;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getMiddleName() {
return middleName;
}
public void setMiddleName(String middleName) {
this.middleName = middleName;
}
@XmlElement(nillable=true)
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
Demo
In the demo code below we will set both the middleName and lastName properties to null. Since we have mapped these properties differently in the domain model we will examine the output to see the impact of using @XmlElement(nillable=true).
package blog.json.nillable;
import javax.xml.bind.*;
public class Demo {
public static void main(String[] args) throws Exception {
Customer customer = new Customer();
customer.setFirstName("Jane");
customer.setMiddleName(null);
customer.setLastName(null);
JAXBContext jc = JAXBContext.newInstance(Customer.class);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
// Output XML
marshaller.marshal(customer, System.out);
// Output JSON
marshaller.setProperty("eclipselink.media-type", "application/json");
marshaller.marshal(customer, System.out);
}
}
XML Output
By default JAXB implementations do not include null values in the output, so there is no element corresponding to the middleName property. Since we annotated the lastName property with @XmlElement(nillable=true) and it had a null value, it is represented in the output. In XML an element with a null value is represented by adding the xsi:nil="true" attribute.
<?xml version="1.0" encoding="UTF-8"?> <customer> <firstName>Jane</firstName> <lastName xsi:nil="true" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/> </customer>
JSON Output
Just like in the XML output, an entry for the middleName property does not appear in the JSON output. Since we annotated the lastName property with @XmlElement(nillable=true) and it had a null value, it is represented in the output. In JSON a null value is represented with null.
{
"customer" : {
"firstName" : "Jane",
"lastName" : null
}
}
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