Note: I'm the EclipseLink JAXB (MOXy) lead and a member of the JAXB (JSR-222) expert group.
By default MOXy like other JAXB implementations will not marshal an element for null values:
POSSIBLE PROBLEM
I believe the strIpAddress property is not null, but contains a value of empty String (""). This would cause the empty element to be written out.
Root
package forum11215485;
import javax.xml.bind.annotation.*;
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Root {
String nullValue;
String emptyStringValue;
String stringValue;
}
Demo
package forum11215485;
import javax.xml.bind.*;
public class Demo {
public static void main(String[] args) throws Exception {
JAXBContext jc = JAXBContext.newInstance(Root.class);
Root root = new Root();
root.nullValue = null;
root.emptyStringValue = "";
root.stringValue = "Hello World";
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(root, System.out);
}
}
Output
Note how there is no element marshalled out for the nullValue field, and the emptyStringValue field is marshalled as an empty element.
<?xml version="1.0" encoding="UTF-8"?>
<root>
<emptyStringValue></emptyStringValue>
<stringValue>Hello World</stringValue>
</root>
SOLUTION #1 - Ensure the property is set to null and not ""
SOLUTION #2 - Write an XmlAdapter that converts "" to null
An XmlAdapter is a JAXB mechanism that allows an object to be marshalled as another object.
StringAdapter
The following XmlAdapter will marshal empty strings as null. This will cause them not to appear in the XML representation.
package forum11215485;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public class StringAdapter extends XmlAdapter<String, String> {
@Override
public String unmarshal(String v) throws Exception {
return v;
}
@Override
public String marshal(String v) throws Exception {
if(null == v || v.length() == 0) {
return null;
}
return v;
}
}
package-info
The XmlAdapter is hooked in using the @XmlJavaTypeAdapter annotation. Below is an example of hooking it in at the package level so that it applies to a fields/properties of type String within the package. For more information see: http://blog.bdoughan.com/2012/02/jaxb-and-package-level-xmladapters.html
@XmlJavaTypeAdapter(value=StringAdapter.class, type=String.class)
package forum11215485;
import javax.xml.bind.annotation.adapters.*;
Output
Now the output from running the demo code is the following:
<?xml version="1.0" encoding="UTF-8"?>
<root>
<stringValue>Hello World</stringValue>
</root>
