java - How to add DOCTYPE and xml processing instructions when marshalling with JAXB?

Question

I am marshalling (serializing) JAXB beans to output stream. How can I add DOCTYPE declaration and xml processing instructions to ouput?

I am doing currently marshalling like this:

JAXBContext jaxbContext = JAXBContext.newInstance("com.example.package");
Marshaller marshaller = jaxbContext.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);

SchemaFactory schemaFactory = SchemaFactory.newInstance("http://www.w3.org/2001/XMLSchema");
Schema schema = schemaFactory.newSchema(schemaSource);
marshaller.setSchema(schema);

marshaller.marshal(object, output);

I'd like have output that looks something like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE Something SYSTEM "some.dtd">
<?xml-stylesheet type="text/xsl" href="some.xsl"?>

JAXB bean are generated code so I don't want to change them.

There are some hacks and undocumented tricks (see Making JAXB generate an XML processing instruction) to add the xml processing instructions and doctype. But what is the preferred or right way to do this?

Answer 1

The JAXB RI has a proprietary Marshaller property com.sun.xml.bind.xmlHeaders (see XML Preamble Control:

This property allows you to specify an XML preamble (<?xml ...> declaration) and any additional PIs, comments, DOCTYPE declaration that follows it. This property takes effect only when you are marshalling to OutputStream, Writer, or StreamResult. Note that this property interacts with the Marshaller.JAXB_FRAGMENT property. If that property is untouched or set to false, then JAXB would always write its XML preamble, so this property can be only used to write PIs, comments, DOCTYPE, etc. On the other hand, if it is set to true, then JAXB will not write its own XML preamble, so this property may contain custom XML preamble.

This should do what you need. If you're using Java5 and the JAXB RI, then this should just work. If you're using Java6 with its included JAXB implementation, the com.sun.xml.bind.xmlHeaders name might be different, so try com.sun.xml.internal.bind.xmlHeaders instead.