21.What Is XML Binding?
22.Why Use XML Binding?
23.What are the goals of JAXB?
Easy to use
– require minimal XML knowledge – don’ t require SAX/DOM knowledge • Customizable – can customize mapping of XML to Java • Portable – can change JAXB implementation without changing source code • Deliver soon – deliver core functionality ASAP • Natural – follow standard design and naming conventions in generated Java • Match schema – easy to identify generated Java components that correspond to schema features • Hide plumbing – encapsulate implementation of unmarshalling, marshalling and validation • Validation on demand – validate objects without requiring marshalling • Preserve object equivalence (round tripping) – marshalling objects to XML and unmarshalling back to objects results in equivalent objects 24.What are the disadvantages/non-goals of JAXB?
• Standardize generated Java
– classes generated by different JAXB implementations may not be compatible with each other • Preserve XML equivalence – unmarshalling XML to objects and marshalling back to XML may not result in equivalent XML • Bind existing JavaBeans to schemas – can only marshal and unmarshal classes generated by JAXB – may be added later • Schema evolution support – can’ t modify previously generated code to support schema changes – must generated new code • Allow generated Java to access XML elements/attributes not described in initial schema • Partial binding – unmarshalling only a subset of an XML document breaks round tripping • Implement every feature of the schema language – it’ s tough to implement all of XML Schema! • Support DTDs – focusing on XML Schema – DTDs were supported in an earlier version, but won’ t be anymore – tools for converting DTDs to XML Schemas exist 25.Give me an example of XSD.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema elementFormDefault="qualified"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns="http://www.withoutbook.com/cars"
targetNamespace="http://www.withoutbook.com/cars">
<xs:complexType name="car">
<xs:sequence>
<xs:element name="make" type="xs:string"/>
<xs:element name="model" type="xs:string"/>
<xs:element name="color" type="xs:string"/>
</xs:sequence>
<xs:attribute name="year" type="xs:positiveInteger" use="required"/>
</xs:complexType>
<xs:element name="cars">
<xs:complexType>
<xs:sequence>
<xs:element name="car" type="car" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
26.Give me an example of XML document?
<?xml version="1.0" encoding="UTF-8"?>
<cars xmlns="http://www.withoutbook.com/cars"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.withoutbook.com/cars cars.xsd">
<car year="2001">
<make>BMW</make>
<model>Z3</model>
<color>yellow
</car>
<car year="2001">
<make>Honda</make>
<model>Odyssey</model>
<color>green</color>
</car>
<car year="1997">
<make>Saturn</make>
<model>SC2</model>
<color>purple
</car>
</cars>
27.How to generate Java from XML Schema. Please show the example.
From command-line
– Windows: %JAXB_HOME%\bin\xjc cars.xsd – UNIX: %JAXB_HOME%/bin/xjc.sh cars.xsd – these write generated files to current directory • From Ant <java jar="${env.JAXB_HOME}/lib/jaxb-xjc.jar" fork="yes"> <arg line="-d ${gen.src.dir} cars.xsd"/> </java> Generated Files: • com/withoutbook/cars directory – Car.java • interface representing the “car” complex type • only describes get and set methods for car properties – Cars.java • interface representing “cars” global element • extends CarsType and javax.xml.bind.Element (just a marker interface) • describes no additional methods – CarsType.java • interface representing anonymous complex type defined inside the “cars” global element • provides method to get collection of Car objects (as a java.util.List) – ObjectFactory.java • class used to create objects of the above interface types • extends DefaultJAXBContextImpl which extends JAXBContext – bgm.ser • a serialized object of type com.sun.msv.grammar.trex.TREXGrammar • can’t find any documentation on this - don’t know its purpose – jaxb.properties • sets a property that defines the class used to create JAXBContext objects • com/withoutbook/cars/impl directory – CarImpl.java • class that implements Car • corresponds to the “car” XML Schema complexType – CarsTypeImpl.java • class that implements CarType • corresponds to the XML Schema anonymous type inside the “cars” element – CarsImpl.java • class that extends CarsTypeImpl and implements Cars • corresponds to the “cars” XML Schema element 28.How to unmarshall XML into Java objects? Convert from XML to Java objects?
Example
ObjectFactory factory = new ObjectFactory(); Unmarshaller u = factory.createUnmarshaller(); Cars cars = (Cars) u.unmarshal(new FileInputStream("cars.xml")); • unmarshal method accepts – java.io.File – java.io.InputStream – java.net.URL – javax.xml.transform.Source • related to XSLT – org.w3c.dom.Node • related to DOM – org.xml.sax.InputSource • related to SAX • Other Unmarshaller methods – void setValidating(boolean validating) • true to enable validation during unmarshalling; false to disable (the default) – boolean setEventHandler(ValidationEventHandler handler) • handleEvent method of ValidationEventHandler is called if validation errors are encountered during unmarshalling • default handler terminates marshalling after first error • return true to continue unmarshalling • return false to terminate with UnmarshalException • see discussion of ValidationEventCollector later 29.Java code for marshalling Java objects into XML?
Example
Marshaller m = factory.createMarshaller(); m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE); Writer fw = new FileWriter("newCars.xml"); m.marshal(cars, fw); • marshal method accepts – java.io.OutputStream – java.io.Writer – javax.xml.transform.Result • related to XSLT – org.w3c.dom.Node • related to DOM – org.xml.sax.ContentHandler • related to SAX • Other Marshaller methods – boolean setEventHandler(ValidationEventHandler handler) • same as use with Unmarshaller, but validation events are delivered during marshalling – void setProperty(String name, Object value) • supported properties are – jaxb.encoding - value is a String » the encoding to use when marshalling; defaults to “UTF-8” – jaxb.formatted.output - value is a Boolean » true to output line breaks and indentation; false to omit (the default) – jaxb.schemaLocation - value is a String » to specify xsi:schemaLocation attribute in generated XML – jaxb.noNamespaceSchemaLocation - value is a String » to specify xsi:noNamespaceSchemaLocation attribute in generated XML 30.Java example/java program to set object for generating XML?
Cars cars = factory.createCars();
Car car = factory.createCar(); car.setColor("blue"); car.setMake("Mazda"); car.setModel("Miata"); car.setYear(BigInteger.valueOf(2012)); cars.getCar().add(car); car = factory.createCar(); car.setColor("red"); car.setMake("Ford"); car.setModel("Mustang II"); car.setYear(BigInteger.valueOf(2011)); cars.getCar().add(car); 31.How to validate java objects?
The graph of Java objects can contain invalid data
– could occur when objects created by unmarshalling are modified – could occur when objects are created from scratch • Use a Validator to validate the objects • Example Validator v = factory.createValidator(); try { v.validateRoot(cars); v.validate(car); } catch (ValidationException e) { // Handle the validation error described by e.getMessage(). } • Other Validator methods – boolean setEventHandler(ValidationEventHandler handler) • handleEvent method of ValidationEventHandler is called if validation errors are encountered • default handler terminates marshalling after first error • return true to continue validating • return false to terminate with ValidationException Pass an instance of javax.xml.bind.util.ValidationEventCollector (in jaxb-api.jar) to setEventHandler to collect validation errors and query them later instead of handling them during validation. ValidationEventCollector vec = new ValidationEventCollector(); v.setEventHandler(vec); v.validate(cars); ValidationEvent[] events = vec.getEvents(); 32.Customizing Type Bindings?
Default bindings can be overridden
– at global scope – on case-by-case basis • Customizations include – names of generated package, classes and methods – method return types – class property (field) types – which elements are bound to classes, as opposed to being ignored – class property to which each attribute and element declaration is bound 33.Syntax of customization?
Customizations can be specified in
– the XML Schema (our focus) – a binding declarations XML document (not well supported by RI yet) • The XML Schema must declare the JAXB namespace and version <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema” xmlns:jxb="http://java.sun.com/xml/ns/jaxb" jxb:version="1.0"> • Customization elements are placed in annotation elements <xsd:annotation> <xsd:appinfo> binding declarations </xsd:appinfo> </xsd:annotation> 34.. Discuss Customization Levels?
Customizations can be made at four levels
– global • defined at “top level” in a <jxb:globalBindings> element • applies to all schema elements in the source schema and in all included/imported schemas (recursively) – schema • defined at “top level” in a <jxb:schemaBindings> element • applies to all schema elements in the target namespace of the source schema – definition • defined in a type or global declaration • applies to all schema elements that reference the type or global declaration – component • defined in a particular schema element or attribute declaration • applies only to it 35.Discuss Global Bindings attributes?– “indexed” (uses array and provides methods to get/set elements) or fully-qualified-java-class-name(must implement java.util.List) – default is “java.util.ArrayList” • enableFailFastCheck – “true” or “false” (default) – if true, invalid property values are reported as soon as they are set, instead of waiting until validation is requested – not implemented yet in RI • generateIsSetMethod – “true” or “false” (default) – if true, generates isSet and unSet methods for the property • underscoreBinding – “asCharInWord” or “asWordSeparator” (default) – if “asWordSeparator” , underscores in XML names are removed and words are camel-cased to form Java name – for example, “gear_shift_knob” goes to “gearShiftKnob” • bindingStyle (was modelGroupAsClass) – “modelGroupBinding” or “elementBinding” (default) • choiceContentProperty – “true” or “false” (default) – allows objects to hold one of a number of property choices which may each have a different data type • enableJavaNamingConventions – “true” (default) or “false” • fixedAttributeAsConstantProperty – “true” or “false” (default) – if true, “fixed” attributes will be represented as constants • typesafeEnumBase – “xsd:string” , “xsd:decimal” , “xsd:float” , “xsd:double” or “xsd:NCName” (default) – defines field type used to represent enumerated values in generated typesafe enum class • typesafeEnumMemberName – “generateName” or “generateError” (default) – specifies what to do if an enumerated value cannot be mapped to a valid Java identifier – “generateName” generates names in the form VALUE_# – “generateError” reports an error 36.What is the syntax of schemaBindings?
The syntax for the schemaBindings element is
<jxb:schemaBindings> <jxb:package [name="package-name"]> <jxb:javadoc> ... javadoc ... </jxb:javadoc> </package> <jxb:nameXmlTransform> <jxb:typeName prefix="prefix" suffix="suffix"/> <jxb:elementName prefix="prefix" suffix="suffix"/> <jxb:modelGroupName prefix="prefix" suffix="suffix"/> <jxb:anonymousTypeName prefix="prefix" suffix="suffix"/> </jxb:nameXmlTransform> </jxb:schemaBindings> – every element and attribute within schemaBindings is optional 37.?
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