JAXB: How to customize Xml serialization of double fields

Question

I have a legacy class, with a lot of public double fields. All double fields are initialized with Double.MAX_VALUE to indicate that they are empty. (The legacy serialization is coded to ignore the field and not serialize if field is equals to Double.MAX_VALUE).

We are now trying to serialize this class to Xml using JAXB Marshaller. It is working fine, except that we want to prevent generating Xml for fields which equal Double.MAX_VALUE.

We aren't using a separate JAXB schema, just marking up our classes with various javax.xml.bind.annotation Annotations. If a schema is used, you can add a <javaType> element to specify a custom DataType converter. Is there any way to do this using Annotations or programmatically?

After trying approach recommended below, I still can't get XmlAdapter picked up:

@XmlJavaTypeAdapters({
@XmlJavaTypeAdapter(value=EmptyDoubleValueHandler.class, type=Double.class), @XmlJavaTypeAdapter(value=EmptyDoubleValueHandler.class, type=double.class)})
package tta.penstock.data.iserver;

import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapters;

My top level class is: tta.penstock.data.iserver.OrderBlotter, which contains a list of tta.penstock.data.iserver.OrderResponseWrappers which extends com.eztech.OrderResponse. All the double fields are contained in com.eztech.OrderResponse.

My unit test code does the following:

JAXBContext context = JAXBContext.newInstance(new Class[] { OrderBlotter.class, OrderResponseWrapper.class, OrderResponse.class});

Marshaller marshaller = context.createMarshaller();
StringWriter stringWriter = new StringWriter();
marshaller.marshal(blotter, stringWriter);
System.out.println("result xml=\n" + stringWriter.toString());

But the double values still don't get handled by the XmlAdapter. I know I'm missing something basic, but I'm not sure what it is.

Answer 1

You could use an XmlAdapter:

• http://bdoughan.blogspot.com/2010/07/xmladapter-jaxbs-secret-weapon.html

The XmlAdapter

package example;

import javax.xml.bind.annotation.adapters.XmlAdapter;

public class DoubleAdapter extends XmlAdapter<Double, Double>{

    @Override
    public Double unmarshal(Double v) throws Exception {
        return v;
    }

    @Override
    public Double marshal(Double v) throws Exception {
       if(Double.MAX_VALUE == v) {
           return null;
       } else {
           return v;
       }
    }

}

The Model Object

package example;

import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlRootElement
public class Root {

    @XmlJavaTypeAdapter(DoubleAdapter.class)
    public Double maxDouble = Double.MAX_VALUE;

    @XmlJavaTypeAdapter(DoubleAdapter.class)
    public Double aDouble = 123d;

}

Demo Code

package example;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Root.class);
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(new Root(), System.out);
    }

}

UPDATE

StaxMan's suggestion is a good one. If you specify the following package level annotation you can avoid the need of individually annotating all the Double properties

package-info.java

@XmlJavaTypeAdapters({
    @XmlJavaTypeAdapter(type=Double.class, value=DoubleAdapter.class)
})
package example;

import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapters;