Module jakarta.xml.bind
Package jakarta.xml.bind

Interface Unmarshaller

All Known Implementing Classes:
AbstractUnmarshallerImpl
public interface Unmarshaller
The Unmarshaller class governs the process of deserializing XML data into newly created Java content trees, optionally validating the XML data as it is unmarshalled. It provides an overloading of unmarshal methods for many different input kinds.

Unmarshalling from a File: 

       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();
       Object o = u.unmarshal( new File( "nosferatu.xml" ) );

Unmarshalling from an InputStream: 

       InputStream is = new FileInputStream( "nosferatu.xml" );
       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();
       Object o = u.unmarshal( is );

Unmarshalling from a URL: 

       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();
       URL url = new URL( "http://beaker.east/nosferatu.xml" );
       Object o = u.unmarshal( url );

Unmarshalling from a StringBuffer using a javax.xml.transform.stream.StreamSource: 


       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();
       StringBuffer xmlStr = new StringBuffer( "<?xml version="1.0"?>..." );
       Object o = u.unmarshal( new StreamSource( new StringReader( xmlStr.toString() ) ) );

Unmarshalling from a org.w3c.dom.Node: 

       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();

       DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
       dbf.setNamespaceAware(true);
       DocumentBuilder db = dbf.newDocumentBuilder();
       Document doc = db.parse(new File( "nosferatu.xml"));

       Object o = u.unmarshal( doc );

Unmarshalling from a javax.xml.transform.sax.SAXSource using a client specified validating SAX2.0 parser: 

       // configure a validating SAX2.0 parser (Xerces2)
       static final String JAXP_SCHEMA_LANGUAGE =
           "http://java.sun.com/xml/jaxp/properties/schemaLanguage";
       static final String JAXP_SCHEMA_LOCATION =
           "http://java.sun.com/xml/jaxp/properties/schemaSource";
       static final String W3C_XML_SCHEMA =
           "http://www.w3.org/2001/XMLSchema";

       System.setProperty( "javax.xml.parsers.SAXParserFactory",
                           "org.apache.xerces.jaxp.SAXParserFactoryImpl" );

       SAXParserFactory spf = SAXParserFactory.newInstance();
       spf.setNamespaceAware(true);
       spf.setValidating(true);
       SAXParser saxParser = spf.newSAXParser();

       try {
           saxParser.setProperty(JAXP_SCHEMA_LANGUAGE, W3C_XML_SCHEMA);
           saxParser.setProperty(JAXP_SCHEMA_LOCATION, "http://....");
       } catch (SAXNotRecognizedException x) {
           // exception handling omitted
       }

       XMLReader xmlReader = saxParser.getXMLReader();
       SAXSource source =
           new SAXSource( xmlReader, new InputSource( "http://..." ) );

       // Setup Jakarta XML Binding to unmarshal
       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();
       ValidationEventCollector vec = new ValidationEventCollector();
       u.setEventHandler( vec );

       // turn off the Jakarta XML Binding provider's default validation mechanism to
       // avoid duplicate validation
       u.setValidating( false )

       // unmarshal
       Object o = u.unmarshal( source );

       // check for events
       if( vec.hasEvents() ) {
          // iterate over events
       }

Unmarshalling from a StAX XMLStreamReader: 

       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();

       javax.xml.stream.XMLStreamReader xmlStreamReader =
           javax.xml.stream.XMLInputFactory().newInstance().createXMLStreamReader( ... );

       Object o = u.unmarshal( xmlStreamReader );

Unmarshalling from a StAX XMLEventReader: 

       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();

       javax.xml.stream.XMLEventReader xmlEventReader =
           javax.xml.stream.XMLInputFactory().newInstance().createXMLEventReader( ... );

       Object o = u.unmarshal( xmlEventReader );

Unmarshalling XML Data

Unmarshalling can deserialize XML data that represents either an entire XML document or a subtree of an XML document. Typically, it is sufficient to use the unmarshalling methods described by Unmarshal root element that is declared globally. These unmarshal methods utilize JAXBContext's mapping of global XML element declarations and type definitions to Jakarta XML Binding mapped classes to initiate the unmarshalling of the root element of XML data. When the JAXBContext's mappings are not sufficient to unmarshal the root element of XML data, the application can assist the unmarshalling process by using the unmarshal by declaredType methods. These methods are useful for unmarshalling XML data where the root element corresponds to a local element declaration in the schema.
An unmarshal method never returns null. If the unmarshal process is unable to unmarshal the root of XML content to a Jakarta XML Binding mapped object, a fatal error is reported that terminates processing by throwing JAXBException.

Unmarshal a root element that is globally declared

The unmarshal methods that do not have an declaredType parameter use JAXBContext to unmarshal the root element of an XML data. The JAXBContext instance is the one that was used to create this Unmarshaller. The JAXBContext instance maintains a mapping of globally declared XML element and type definition names to Jakarta XML Binding mapped classes. The unmarshal method checks if JAXBContext has a mapping from the root element's XML name and/or @xsi:type to a Jakarta XML Binding mapped class. If it does, it umarshalls the XML data using the appropriate Jakarta XML Binding mapped class. Note that when the root element name is unknown and the root element has an @xsi:type, the XML data is unmarshalled using that Jakarta XML Binding mapped class as the value of a JAXBElement. When the JAXBContext object does not have a mapping for the root element's name nor its @xsi:type, if it exists, then the unmarshal operation will abort immediately by throwing a UnmarshalException. This exception scenario can be worked around by using the unmarshal by declaredType methods described in the next subsection.

Unmarshal by Declared Type

The unmarshal methods with a declaredType parameter enable an application to deserialize a root element of XML data, even when there is no mapping in JAXBContext of the root element's XML name. The unmarshaller unmarshals the root element using the application provided mapping specified as the declaredType parameter. Note that even when the root element's element name is mapped by JAXBContext, the declaredType parameter overrides that mapping for deserializing the root element when using these unmarshal methods. Additionally, when the root element of XML data has an xsi:type attribute and that attribute's value references a type definition that is mapped to a Jakarta XML Binding mapped class by JAXBContext, that the root element's xsi:type attribute takes precedence over the unmarshal methods declaredType parameter. These methods always return a JAXBElement<declaredType> instance. The table below shows how the properties of the returned JAXBElement instance are set.
Unmarshal By Declared Type returned JAXBElement
JAXBElement Property Value
name xml element name
value instanceof declaredType
declaredType unmarshal method declaredType parameter
scope null (actual scope is unknown)

The following is an example of unmarshal by declaredType method.

Unmarshal by declaredType from a org.w3c.dom.Node: 


       Schema fragment for example
       <xs:schema>
          <xs:complexType name="FooType">...<\xs:complexType>
          <!-- global element declaration "PurchaseOrder" -->
          <xs:element name="PurchaseOrder">
              <xs:complexType>
                 <xs:sequence>
                    <!-- local element declaration "foo" -->
                    <xs:element name="foo" type="FooType"/>
                    ...
                 </xs:sequence>
              </xs:complexType>
          </xs:element>
       </xs:schema>

       JAXBContext jc = JAXBContext.newInstance( "com.acme.foo" );
       Unmarshaller u = jc.createUnmarshaller();

       DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
       dbf.setNamespaceAware(true);
       DocumentBuilder db = dbf.newDocumentBuilder();
       Document doc = db.parse(new File( "nosferatu.xml"));
       Element  fooSubtree = ...; // traverse DOM till reach xml element foo, constrained by a
                                  // local element declaration in schema.

       // FooType is the Jakarta XML Binding mapping of the type of local element declaration foo.
       JAXBElement<FooType> foo = u.unmarshal( fooSubtree, FooType.class);

Support for SAX2.0 Compliant Parsers

A client application has the ability to select the SAX2.0 compliant parser of their choice. If a SAX parser is not selected, then the Jakarta XML Binding Provider's default parser will be used. Even though the Jakarta XML Binding Provider's default parser is not required to be SAX2.0 compliant, all providers are required to allow a client application to specify their own SAX2.0 parser. Some providers may require the client application to specify the SAX2.0 parser at schema compile time. See unmarshal(Source) for more detail.

Validation and Well-Formedness

A client application can enable or disable JAXP validation mechanism via the setSchema(javax.xml.validation.Schema) API. Sophisticated clients can specify their own validating SAX 2.0 compliant parser and bypass the JAXP validation mechanism using the unmarshal(Source) API.

Since unmarshalling invalid XML content is defined in Jakarta XML Binding, the Unmarshaller default validation event handler was made more lenient than in JAXB 1.0. When schema-derived code generated by JAXB 1.0 binding compiler is registered with JAXBContext, the default unmarshal validation handler is DefaultValidationEventHandler and it terminates the marshal operation after encountering either a fatal error or an error. For a Jakarta XML Binding client application, there is no explicitly defined default validation handler and the default event handling only terminates the unmarshal operation after encountering a fatal error.

Supported Properties

There currently are not any properties required to be supported by all Jakarta XML Binding Providers on Unmarshaller. However, some providers may support their own set of provider specific properties.

Unmarshal Event Callbacks

The Unmarshaller 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 Jakarta XML Binding mapped classes is triggered during unmarshalling. 'External listeners' allow for centralized processing of unmarshal events in one callback method rather than by type event callbacks.

'Class defined' event callback methods allow any Jakarta XML Binding mapped class to specify its own specific callback methods by defining methods with the following method signature: 

   // This method is called immediately after the object is created and before the unmarshalling of this
   // object begins. The callback provides an opportunity to initialize JavaBean properties prior to unmarshalling.
   void beforeUnmarshal(Unmarshaller, Object parent);

   //This method is called after all the properties (except IDREF) are unmarshalled for this object,
   //but before this object is set to the parent object.
   void afterUnmarshal(Unmarshaller, Object parent);
The class defined 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 Unmarshaller.Listener instance with an setListener(Listener). The external listener receives all callback events, allowing for more centralized processing than per class defined callback methods. The external listener receives events when unmarshalling process is marshalling to a Jakarta XML Binding element or to Jakarta XML Binding mapped class.

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 Unmarshaller.Listener.beforeUnmarshal(Object, Object) and Unmarshaller.Listener.afterUnmarshal(Object, Object).

An event callback method throwing an exception terminates the current unmarshal process.

Since:
1.6, JAXB 1.0
See Also: