Parameterized Types
You'll need the JDK 5.0 to work with parameterized types. With parametrized types, casts are not required and type checking is performed at compile time. Using casts (as in JAXB 1.0) runs the risk of incurring a runtime exception if an object is cast to a type of which is not an instance.
In marshalling an example document that conforms to the example XML Schema in Listing 1, the procedure to add a journal element to a catalog element with JAXB 1.0 is shown below:
ObjectFactory factory=new ObjectFactory();
Catalog catalog=factory.createCatalog();
Journal journal=factory.createJournal();
java.util.List journalList=catalog.getJournal();
journalList.add(journal);
The type of journalList List is determined at run-time. In JAXB 2.0, collection types are specified in the class and are checked at compile-time. So, the procedure to add a journal element to a catalog element with JAXB 2.0 looks like this:
ObjectFactory factory = new ObjectFactory();
CatalogType catalog = factory.createCatalogType();
JournalType journal = factory.createJournalType();
List<JournalType> journalList = catalog.getJournal();
journalList.add(journal);
The Collection journalList's type is specified with the parameterized types notation as JournalType.
In JAXB 1.0, a Java object representing an XML document may be marshaled using the marshal() method:
JAXBContext jaxbContext=JAXBContext.newInstance("generated");
Marshaller marshaller=jaxbContext.createMarshaller();
Catalog catalog=factory.createCatalog();
marshaller.marshal(catalog, new FileOutputStream(xmlDocument));
In JAXB 2.0, you first obtain a JAXBElement object of parameter type CatalogType using the factory class method createCatalog(CatalogType). A JAXBElement object is a JAXB representation of an XML element. Subsequently, you marshal the parameterized JAXBElement with the marshal() method:
JAXBElement<CatalogType≫ catalogElement=factory.createCatalog(catalog);
marshaller.marshal(catalogElement, new FileOutputStream(xmlDocument));
In unmarshalling with JAXB 1.0, the Java object representation of an XML document is obtained with the unmarshal() method:
Unmarshaller unMarshaller=jaxbContext.createUnmarshaller();
Catalog catalog=(Catalog)(unMarshaller.unmarshal(xmlDocument));
With JAXB 2.0, the unmarshal() method returns a parameterized JAXBElement object. In the example, the parameter type is CatalogType. Obtain a CatalogType object from the JAXBElement object using the getValue() method:
Unmarshaller unMarshaller = jaxbContext.createUnmarshaller();
JAXBElement catalogElement =(JAXBElement) unMarshaller.unmarshal(xmlDocument);
CatalogType catalog=catalogElement.getValue();
As you can see, the advantage of using parameterized types in JAXB 2.0 is that type checking is performed at compile time, which means that runtime exceptions won't be generated if type casting has an error.
Validation
Validation is the process of confirming that an XML document conforms to an XML Schema. JAXB 2.0 validation's additional features make it much more flexible than JAXB 1.0's. In JAXB 1.0 validation is available only during the unmarshalling operation, and it is terminated if an error is found. In JAXB 2.0, validation is also available during the marshalling operation, which continues even if a validation error occurs when a custom ValidationEventHandler is used.
In JAXB 1.0, validation is set with the setValidating() method:
unMarshaller.setValidating();
In JAXB 2.0, the setValidating() method has been deprecated. Now, schema validation is performed using the JAXP 1.3 validation API. To validate using JAXB 2.0, create a SchemaFactory object using the static method newInstance(String). The String parameter of newInstance(String) method specifies the schema language used for schema validation (click here for more information on the XML schema language). Create schema object from the SchemaFactory object using the method newSchema(File). The File parameter of the newSchema() method represents a File object representation of an XML document. A schema object may also be created from a DOMSource, SAXSource, StreamSource, or a URL object representation of an XML schema file. Set the schema on the Unmarshaller object using setSchema(Schema) method. A custom ValidationEventHandler may also be specified using the setEventHandler(ValidationEventHandler handler) method.
SchemaFactory schemaFactory=SchemaFactory.newInstance
("http://www.w3.org/2001/XMLSchema");
Schema schema=schemaFactory.newSchema(new File("catalog.xsd"));
unMarshaller.setSchema(schema);
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