Presentacipon de JAXB

8/10/2019 Presentacipon de JAXB

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The Java

Architecture ForXML Binding (JAXB)

By:Yoav Zibin

Sharon Krisher


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Motivation for JAXB

The main purpose of XML Schemais: Validationof XML documents

Any other purposes? Hint 1: determinism requirement

Hint 2: the default attribute has nothingto dowith validation


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Motivation for JAXB

Problem: How to manipulate this data model?

DOM(data object model) solution:

Pros:simple, general (a schema is not even required) Cons:no types, no compile-time checking

I wish to write

root.getChild("Address").getChild("Number").getText()

DOMpseudo-code example

root.getAddress().getNumber()

returns a number

returns a string


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Binding Compiler

Javainterface

s

Sourceschema

JAXB solution:

Mapping XML Schema to Java interfaces

Pros:preserve types, compile-time checking

Cons:complex, specific to a certain schema


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Binding Compiler

public interfaceAddressType{

longgetNumber();

void setNumber(longvalue);

StringgetStreet();

void setStreet(Stringvalue);

}

Must be non-negative

Must be non-null


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Main Features

Unmarshal:xmlobjects

Create / Read / Update / Delete objects

Validateobjects

Marshal:objectsxml

No roundtripguarantees Marshal( Unmarshal(xml) ) xml

We found that order is not always preserved

But usually roundtrip holds


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Step 1: Create XML Schema


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Step 2: Create XML Document

Sharon Krisher

Iben Gevirol

57

Moshe Sharet89

Check that your XML conforms to the Schema

Demo.xml


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Step 3: Run the binding compiler

%JWSDP_HOME%\jaxb\bin\xjc -p demodemo.xsd

A package named demois created

(in the directory demo) The package contains (among other things):

interfaceAddressType

interface PersonType


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AddressType and PersonType

public interfaceAddressType{

long getNumber();

void setNumber(long value);

String getStreet();void setStreet(String value);

}

public interface PersonType{

String getName();

void setName(String value);

/* List ofAddressType*/

java.util.List getAddress();

}

In Java1.5:List

Must contain at least one item

Must be non-negative

Must be non-null

Must be non-null


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Step 4: Create Context

The context is the entry point to the API

Contains methods to create Marshaller,

Unmarshaller and Validator instances

JAXBContext context= JAXBContext.newInstance("demo");

The package name is demo

(Recall: xjc -p demodemo.xsd)


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Step 5: Unmarshal: xml -> objects

Unmarshallerunmarshaller=

context.createUnmarshaller();

unmarshaller.setValidating(true);

PersonTypeperson=

(PersonType) unmarshaller.unmarshal(

new FileInputStream("demo.xml") );

Enable validation of xml

according to the

schema whileunmarshalling


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Step 6: Read

System.out.println("Person name=" +

person.getName() );

AddressTypeaddress= (AddressType)

person.getAddress().get(0);

System.out.println("First Address: " +

" Street=" + address.getStreet() +" Number=" + address.getNumber() );


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Step 7: Manipulate objects

// Update

person.setName("Yoav Zibin");

// Delete

ListaddressList=person.getAddress();

addressList.clear();

part of the demo package

uses the factory pattern

// Create

ObjectFactoryobjectFactory= new ObjectFactory();

AddressTypenewAddr= objectFactory.createAddressType();

newAddr.setStreet("Hanoter");

newAddr.setNumber(5);

addressList.add( newAddr);

What happens if we validate there?


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Step 8: Validate on-demand

Validatorvalidator= context.createValidator();

validator.validate(newAddr);

validator.validate(person);

Check that we have set StreetandNumber,

and thatNumberis non-negative

Check that we have setName, and thatAddress

contains at least one item


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Step 9: Marshal: objects -> xml

Marshallermarshaller= context.createMarshaller();

marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT,

Boolean.TRUE);

marshaller.marshal(person,new FileOutputStream("output.xml"));

Yoav Zibin

Hanoter

5

output.xml


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And now, the Demo!


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First Part Summary


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Similar Technologies

Liquid XML Data Binding

Similar to JAXB

Supports all Schemaconstructs

In addition to Java: C#, C++, Visual Basic 6

Relaxer

Instead of Schemauses Relax

Castor.org


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Second Part Outline

Validation

MappingXML Schema to Java

Naming

Java Properties

Simple and Complex Types

Customization of the default mapping


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Validation Constraints

Three categories of constraints

Type constraints: Legal values in simple types

E.g., in every address, numberis a non-negativeinteger

Local structural constraints E.g., in every person, addresscontains at least

one item Global structural constraints

E.g., ID and IDREF


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Validation

Three forms of validation Unmarshal timevalidation (at unmarshal time)

On-demandvalidation (at any chosen point in time) validateRoot(object) vs. validate(object) validateRoot includes global constraint checking

Fail-fastvalidation (at all times) Currently not implemented

Checks that the value provided to a set method is legal

When validation errors occur an event is raised(no exception) and validation continues, so thatseveral validation errors can be handled.

Default handler raises an exception on first error


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Unsupported Schema Concepts

Substitution groups

Type substitutions (xsi:type, block)

Key, keyref, and unique

anyAttribute

No support for XPath or any other query

langauge


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Element vs. Type

An element also has a qualified name

When is the difference important? (next)

interface UglyManextends PersonType, Element{}interface PrettyWoman extends PersonType, Element{}

interface PersonType{ }

an empty interface which marks

the existence of a static QName


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When must I use elements?

Marshal:

General content

marshaller.marshal(Object, OutputStream)

must be an element,

otherwise the resulting

output is not a legal XML

ObjectgetAny();

void setAny(Object elementOrValue);

Sharon Krisher

Iben Gevirol

57

E.g., when we marshal a PersonType:


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Naming

Problem: sometimes XML names

are not legaljava names

do not comply to java naming standards

The binding compiler creates proper

names

XML Name Class Name Method Name

mixedCaseName MixedCaseName getMixedCaseName

name-with-dash NameWithDash getNameWithDash

aa_bb-cc AaBbCc getAaBbCc


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Java Properties

Local schema components are mapped to:

Simple property (get, set)

With customization: isSetName, unsetName

List property

Indexed property (next)

java.util.ListgetAddress();

StringgetName();

void setName(Stringvalue);

In Java1.5:

List


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Indexed Property

Used instead of a list property when a

proper customization is applied

AddressType[] getAddress();

void setAddress(AddressType[] value);

AddressTypegetAddress(int index);

void setAddress(int index,AddressTypevalue);


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General Content Property

The most general content property

Can represent any content, however complex

A list that can contain element interfaces and values Used for problematic cases :

Name collisions due to derivation

Mixedcontent

Another example:

ListgetAny();

Each item can be

some element or

value


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Simple Types (partial diagram)

SimpleType

Primtive List Union Restriction

ID/IDREF

maxInclusive

Enumeration

date

integer

int

Calendar

BigInteger

int

String/Object

ListRepresented as

validation

constraints

Next (1)

Next (2)


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Simple Type: Union

Public interface Date {ObjectgetMonth();

void setMonth(Object);

}

Common supertype of(Integer, String) isObject


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Type Safe Enumeration

public class USState{protected USSate(String v) {}

public static final USStateAK= ;public static final USStateNY= ;

public StringgetValue();

public static USStatefromValue(Stringv) {}}


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XML Schema Type System

Any

SimpleType ComplexType

SimpleContent ComplexContent Sequence Choice All

Extension Extension

RestrictionAttributes

use

default

fixed

Elements

abstractnillable

minOccurs

maxOccurs

finishedRepresented as

a Java interface

The interface

extendsthe base

types interface Represented as

Java properties

*

* *

( ) Next*

**

*


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Complex Types

Represented as a Java interface

Anonymous type

An interface is created.

The name is derived from the name of the

schema element + Type, e.g Foo FooType

Abstract types: no create method inObjectFactory


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Complex Type:Simple Content

interface InternationalPrice{

intgetValue();

void setValue(int);

StringgetCurrency();

void setCurrency(String);

}


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Complex Type:Aggregation

interface Foo{

intgetA(); void setA(int);intgetB(); void setB(int);

intgetC(); void setC(int);

}


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Complex Type:Mixed Content


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Complex Type: Choice

public interface FooBarType{

ObjectgetFooOrBar();

void setFooOrBar(Object);

}

Common supertype of(Integer, String) isObject

Similar tounion

public interface FooBarType{

intgetFoo();

void setFoo(intvalue);

StringgetBar();

void setBar(Stringvalue);

boolean isSetFoo();

void unsetFoo();

boolean isSetBar();

void unsetBar();

}

The programmer

is responsible to

only set one ofFoo or Bar

Default

Customization (Not implemented yet)


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When maxOccurs>1

public interface FooBarType {

interface Fooextends Element{}

interface Barextends Element{}

// Items are instances of Fooand BarListgetFooOrBar();

}

For asequence: ListgetFooAndBar()

The programmer needs to make sure that

the list contains sequences of.


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Complex Type:All

Mapped like Sequence

Cant have maxOccurs > 1

No way to specify the orderof elements Round tripdoesnt hold (orderis not preserved):

XML

Objects

in

memoryXML

unmarshal

marshal


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Nillable elements

IntegergetAge();void setAge(Integervalue);

XML: 25 or

setAge

(null

)

Java:setAge

( newInteger

(25) )

or


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Customization

Used to augment the default mapping

Customizations declared via special xml

tags

May appear inside the source schema or

in a separate file


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Uses of Customization

Change default names of interfaces and

properties

For a specific schema construct For an entire namespace

Add a suffix or a prefix

Change the types of propertiesAdd javadoc declarations


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Software Engineering Issues

Weak Typing

Our suggestions:

Marshal / Unmarshal : Object Element IDREF: Object Identifiable

Sometimes JAXB doesnt allow us to

control the order of elements Example 1: xs:all

Example 2: next slide


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Element Order Example


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Its the programmers fault

Taken from JAXB specification:

The caller must be sure

There is an expectation User is responsible

unexpected behavior may occur.

42obj.setAge(42);

obj.unsetAge();

System.out.println( obj.getAge() );

Question: What is the output ?

obj.setFoo(42);

obj.setBar("A");

System.out.println( obj.isSetFoo() );

xs:choice between Fooand Bar

true


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The END

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