JAXB marshals XML differently to OutputStream vs. StringWriter

Looks like this might be a "bug" in JAXB. Looking at the source, the calls for marshal() create different writers based on the output/writer type parameter:

public void marshal(Object obj, OutputStream out, NamespaceContext inscopeNamespace) throws JAXBException {    write(obj, createWriter(out), new StAXPostInitAction(inscopeNamespace,serializer));}public void marshal(Object obj, XMLStreamWriter writer) throws JAXBException {    write(obj, XMLStreamWriterOutput.create(writer,context), new StAXPostInitAction(writer,serializer));}

The implementations of the writers is different with regards to how they handle "empty elements". The above code is from:

jaxb-ri\runtime\src\com\sun\xml\bind\v2\runtime\MarshallerImpl.java.

The two writers you are creating are:

jaxb-ri\runtime\src\com\sun\xml\bind\v2\runtime\output\UTF8XmlOutput.java

jaxb-ri\runtime\src\com\sun\xml\bind\v2\runtime\output\XMLStreamWriterOutput.java

The good news is that JAXB is a specification with more than one implementation (just like JPA). If one implementation is not meeting your needs, others are available such as EclipseLink JAXB (MOXy):

• http://www.eclipse.org/eclipselink/moxy.php

I don't know why JAXB is doing this - or even if it is JAXB - if JAXB is outputting XML via a SAXContentHandler for example, then it has no direct control over how close tags are produced.

To get consistent behaviour, you could wrap your OutputStream in a OutputStreamWriter, e.g.

   public void marshal(Marshalable obj, OutputStream os) throws XMLMarshalException {        try {            marshaller.marshal(obj, new OutputStreamWriter(os, "UTF-8"));        } catch (JAXBException jaxbe) {            throw new XMLMarshalException(jaxbe);        }    }

Along the same lines, you might see what happens if you wrap the StringWriter in a PrintWriter. Maybe there is some custom code that detects StringWriter to tries to keep the output short as possible. Sounds unlikely, but I have no other explanation.