The Marshaller class is responsible for governing the process
of serializing Java content trees back into XML data. It provides the basic
marshalling methods:
Assume the following setup code for all following code fragments:
JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
Unmarshaller u = jc.createUnmarshaller();
Object element = u.unmarshal( new File( "foo.xml" ) );
Marshaller m = jc.createMarshaller();
Marshalling to a File:
OutputStream os = new FileOutputStream( "nosferatu.xml" );
m.marshal( element, os );
Marshalling to a SAX ContentHandler:
// assume MyContentHandler instanceof ContentHandler
m.marshal( element, new MyContentHandler() );
Marshalling to a DOM Node:
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setNamespaceAware(true);
DocumentBuilder db = dbf.newDocumentBuilder();
Document doc = db.newDocument();
m.marshal( element, doc );
Marshalling to a java.io.OutputStream:
m.marshal( element, System.out );
Marshalling to a java.io.Writer:
m.marshal( element, new PrintWriter( System.out ) );
Marshalling to a javax.xml.transform.SAXResult:
// assume MyContentHandler instanceof ContentHandler
SAXResult result = new SAXResult( new MyContentHandler() );
m.marshal( element, result );
Marshalling to a javax.xml.transform.DOMResult:
DOMResult result = new DOMResult();
m.marshal( element, result );
Marshalling to a javax.xml.transform.StreamResult:
StreamResult result = new StreamResult( System.out );
m.marshal( element, result );
Marshalling to a javax.xml.stream.XMLStreamWriter:
XMLStreamWriter xmlStreamWriter =
XMLOutputFactory.newInstance().createXMLStreamWriter( ... );
m.marshal( element, xmlStreamWriter );
Marshalling to a javax.xml.stream.XMLEventWriter:
XMLEventWriter xmlEventWriter =
XMLOutputFactory.newInstance().createXMLEventWriter( ... );
m.marshal( element, xmlEventWriter );
Marshalling content tree rooted by a JAXB element
The first parameter of the overloaded
Marshaller.marshal(java.lang.Object, ...) methods must be a
JAXB element as computed by
JAXBIntrospector.isElement(java.lang.Object)
;
otherwise, a Marshaller.marshal method must throw a
MarshalException
. There exist two mechanisms
to enable marshalling an instance that is not a JAXB element.
One method is to wrap the instance as a value of a JAXBElement
,
and pass the wrapper element as the first parameter to
a Marshaller.marshal method. For java to schema binding, it
is also possible to simply annotate the instance's class with
@XmlRootElement
.
Encoding
By default, the Marshaller will use UTF-8 encoding when generating XML data
to a java.io.OutputStream, or a java.io.Writer. Use the
setProperty
API to change the output
encoding used during these marshal operations. Client applications are
expected to supply a valid character encoding name as defined in the
W3C XML 1.0
Recommendation and supported by your
Java Platform.
Validation and Well-Formedness
Client applications are not required to validate the Java content tree prior
to calling any of the marshal API's. Furthermore, there is no requirement
that the Java content tree be valid with respect to its original schema in
order to marshal it back into XML data. Different JAXB Providers will
support marshalling invalid Java content trees at varying levels, however
all JAXB Providers must be able to marshal a valid content tree back to
XML data. A JAXB Provider must throw a MarshalException when it
is unable to complete the marshal operation due to invalid content. Some
JAXB Providers will fully allow marshalling invalid content, others will fail
on the first validation error.
Even when schema validation is not explictly enabled for the marshal operation,
it is possible that certain types of validation events will be detected
during the operation. Validation events will be reported to the registered
event handler. If the client application has not registered an event handler
prior to invoking one of the marshal API's, then events will be delivered to
a default event handler which will terminate the marshal operation after
encountering the first error or fatal error. Note that for JAXB 2.0 and
later versions, DefaultValidationEventHandler
is
no longer used.
Supported Properties
All JAXB Providers are required to support the following set of properties.
Some providers may support additional properties.
- jaxb.encoding - value must be a java.lang.String
- The output encoding to use when marshalling the XML data. The
Marshaller will use "UTF-8" by default if this property is not
specified.
- jaxb.formatted.output - value must be a java.lang.Boolean
- This property controls whether or not the Marshaller will format
the resulting XML data with line breaks and indentation. A
true value for this property indicates human readable indented
xml data, while a false value indicates unformatted xml data.
The Marshaller will default to false (unformatted) if this
property is not specified.
- jaxb.schemaLocation - value must be a java.lang.String
- This property allows the client application to specify an
xsi:schemaLocation attribute in the generated XML data. The format of
the schemaLocation attribute value is discussed in an easy to
understand, non-normative form in
Section 5.6
of the W3C XML Schema Part 0: Primer and specified in
Section 2.6 of the W3C XML Schema Part 1: Structures.
- jaxb.noNamespaceSchemaLocation - value must be a java.lang.String
- This property allows the client application to specify an
xsi:noNamespaceSchemaLocation attribute in the generated XML
data. The format of the schemaLocation attribute value is discussed in
an easy to understand, non-normative form in
Section 5.6
of the W3C XML Schema Part 0: Primer and specified in
Section 2.6 of the W3C XML Schema Part 1: Structures.
- jaxb.fragment - value must be a java.lang.Boolean
- This property determines whether or not document level events will be
generated by the Marshaller. If the property is not specified, the
default is false. This property has different implications depending
on which marshal api you are using - when this property is set to true:
marshal(Object,ContentHandler)
- the Marshaller won't
invoke ContentHandler.startDocument()
and
ContentHandler.endDocument()
.
marshal(Object,Node)
- the property has no effect on this
API.
marshal(Object,OutputStream)
- the Marshaller won't
generate an xml declaration.
marshal(Object,Writer)
- the Marshaller won't
generate an xml declaration.
marshal(Object,Result)
- depends on the kind of
Result object, see semantics for Node, ContentHandler, and Stream APIs
marshal(Object,XMLEventWriter)
- the
Marshaller will not generate XMLStreamConstants.START_DOCUMENT
and
XMLStreamConstants.END_DOCUMENT
events.
marshal(Object,XMLStreamWriter)
- the
Marshaller will not generate XMLStreamConstants.START_DOCUMENT
and
XMLStreamConstants.END_DOCUMENT
events.
Marshal Event Callbacks
"The Marshaller
provides two styles of callback mechanisms
that allow application specific processing during key points in the
unmarshalling process. In 'class defined' event callbacks, application
specific code placed in JAXB mapped classes is triggered during
marshalling. 'External listeners' allow for centralized processing
of marshal events in one callback method rather than by type event callbacks.
Class defined event callback methods allow any JAXB mapped class to specify
its own specific callback methods by defining methods with the following method signatures:
// Invoked by Marshaller after it has created an instance of this object.
boolean beforeMarshal(Marshaller, Object parent);
// Invoked by Marshaller after it has marshalled all properties of this object.
void afterMmarshal(Marshaller, Object parent);
The class defined event callback methods should be used when the callback method requires
access to non-public methods and/or fields of the class.
The external listener callback mechanism enables the registration of a Marshaller.Listener
instance with a Marshaller.setListener(Listener)
. The external listener receives all callback events,
allowing for more centralized processing than per class defined callback methods.
The 'class defined' and external listener event callback methods are independent of each other,
both can be called for one event. The invocation ordering when both listener callback methods exist is
defined in Marshaller.Listener.beforeMarshal(Object)
and Marshaller.Listener.afterMarshal(Object)
.
An event callback method throwing an exception terminates the current marshal process.