Altering the XML header produced by the JAXB marshaller

Question

I am currently using the following code to marshal an object into an xml string

    JAXBContext context;

    try {
        context = JAXBContext.newInstance(heartbeat.getClass());
        StringWriter writer = new StringWriter();
        Marshaller marshaller = context.createMarshaller();

        heartbeat.setHeader(header);
        heartbeat.setHeartbeatEvent(event);

        marshaller.marshal(heartbeat, writer);
        String stringXML = writer.toString();
        return stringXML;

    } catch (JAXBException e) {
        throw new RuntimeException("Problems generating XML in specified "
                + "encoding, underlying problem is " + e.getMessage(),
                e);
    }

Which produces the following header

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

My desired output is the following

<?xml version=\"1.0\"?>

By adding this to the marshaller

marshaller.setProperty(Marshaller.JAXB_FRAGMENT, Boolean.FALSE);
marshaller.setProperty("com.sun.xml.bind.xmlHeaders", "<?xml version=\"1.0\"?>");

I receive

<?xml version="1.0" encoding="UTF-8" standalone="yes"?><?xml version="1.0"?>

and changing the JAXB_FRAGMENT property to TRUE removes the header entirely. I have been following the JAXB - Remove 'standalone="yes"' from generated XML thread attempting to solve the problem but I have had no luck so far. Can someone please give me some insight on how to get my desired header from the JAXB marshaller?

Answer 1

In JAXB 3.0.1 the above mentioned constants cause a PropertyException:

 jakarta.xml.bind.PropertyException: name: com.sun.xml.bind.xmlDeclaration value: false

In this case, the XML preamble can be configured with these marshaller constants:

marshaller.setProperty("org.glassfish.jaxb.xmlHeaders", "<?xml version=\"1.0\" encoding=\"UTF-8\" ?>");
marshaller.setProperty(Marshaller.JAXB_FRAGMENT, true);

• https://eclipse-ee4j.github.io/jaxb-ri/3.0.0/docs/ch05.html

Answer 2

When marshalling to an OutputStream using a combination of the following produces the expected output.

    marshaller.setProperty("com.sun.xml.bind.xmlHeaders", "<?xml version=\"1.0\"?>");
    marshaller.setProperty(Marshaller.JAXB_FRAGMENT, true);

The problem you are seeing occurs when you marshal to a Writer, which appears to be a bug in the JAXB reference implementation. You can raise an issue at the link below:

• https://java.net/jira/browse/JAXB/

---

You could always do:

JAXBContext context;

try {
    context = JAXBContext.newInstance(heartbeat.getClass());
    StringWriter writer = new StringWriter();
    writer.append("<?xml version=\"1.0\"?>");
    Marshaller marshaller = context.createMarshaller();
    marshaller.setProperty(Marshaller.JAXB_FRAGMENT, true);

    heartbeat.setHeader(header);
    heartbeat.setHeartbeatEvent(event);

    marshaller.marshal(heartbeat, writer);
    String stringXML = writer.toString();
    return stringXML;

} catch (JAXBException e) {
    throw new RuntimeException("Problems generating XML in specified "
            + "encoding, underlying problem is " + e.getMessage(),
            e);
}

---

EclipseLink JAXB (MOXy) also supports the com.sun.xml.bind.xmlHeaders and it works correctly when marshalling to a Writer (I'm the MOXy lead)

• http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html