Best Practices for Interoperable XML Databinding with JAXB

Best Practices for
Interoperable XML
Databinding with JAXB
Martin Grebac,
SW Engineering Manager, Oracle
(Project METRO)

The following is intended to outline our general product direction. It is intended
for information purposes only, and may not be incorporated into any contract.
It is not a commitment to deliver any material, code, or functionality, and should
not be relied upon in making purchasing decisions. The development, release,
and timing of any features or functionality described for Oracle’s products
remains at the sole discretion of Oracle.

Program Agenda
§ Quick intro
§ Why? The Reasoning
§ General Limitations & W3C approach
§ Common-sense approach
– Complexities to avoid
– The safe intersection
– Examples

Quick Intro

“XML data binding refers to a means of representing
information in an XML document as an object in
computer memory.”
Wikipedia
<Item ItemNumber="2">
<Part PartNumber="456">
<Description> bla bla…</Description>
<Price>13.27</Price>
</Part>
<Quantity>5</Quantity>
</Item>
Item
ItemNumber: 2
Quantity: 5
Part
PartNumber: 456
Description: bla bla …
Price: 13.27

XML DataBinding – Where to Find
§ Direct
– Direct use of JAXB or other Databinding APIs
§ Indirect
– Web Services, JAX-WS, Jersey, REST, …
§ Based on grammar (XML Schema, DTD, RelaxNG, …)
– Classes usually represent the schema structures
– Instances represent content of XML document
– Schema feature set is large

WHY? - The Reasoning

Number of XML Databinding frameworks
§ Axis
§ .NET
§ IBM RAD
§ Mono
§ gSOAP2
§ Castor
§ WCF
§ JAXB
§ XBinder
§ SOAP4R
§ Spring
§ Castor
§ Xbinder
§ Xfire
§ ZSI
§ XMLBeans
§ PHP
§ ADB
§ …

Common XML Databinding Framework
Limitations
§ Round-trip limitations
– Sibling Order
– Physical Structure
– Comments and Processing Instructions
– XML Declaration
§ Feature limitations
– Incomplete schema support
– Transformations
– Document Fragment support

Common XML Databinding Framework
Limitations
§ Round-trip limitations
– Sibling Order
– Physical Structure
– Comments and Processing Instructions
– XML Declaration
§ Feature limitations
– à Incomplete schema support
– Transformations
– Document Fragment support

Do you start from schema?
XML Schema

XML Schema
XML Document

XML Document
Databinding
/
Web Service
framework 1
Objects
XML Schema
Limited
support

Or do you start from classes?
XML Document
Databinding
/
Web Service
framework 2
Databinding
/
Web Service
framework
1
Objects
Objects
XML Schema
Limited
support
Databinding
/
Web Service
framework 3
Objects
Limited
support

Objects

XML Document
Databinding
/
Web Service
framework
1
Objects

XML Document
Databinding
/
Web Service
framework
1
Objects
XML Schema

XML Document
Databinding
/
Web Service
framework 2
Databinding
/
Web Service
framework
1
Objects
Objects
XML Schema
Limited
support

XML Document
Databinding
/
Web Service
framework 2
Databinding
/
Web Service
framework
1
Objects
Objects
XML Schema
Limited
support
Databinding
/
Web Service
framework 3
Objects
Limited
support

Number of XML Databinding frameworks
§ Axis
§ .NET
§ IBM RAD
§ Mono
§ gSOAP2
§ Castor
§ WCF
§ JAXB
§ XBinder
§ SOAP4R
§ Spring
§ Castor
§ Xbinder
§ Xfire
§ ZSI
§ XMLBeans
§ PHP
§ ADB
§ …

LOOKS PRETTY BAD …

… I’M DEPRESSED.

… I’M DEPRESSED.
NOW WHAT?

Now what?
The W3C Approach

W3C – The Ultimate Response
§ Basic XML Schema Patterns for Databinding ~80
– http://www.w3.org/TR/xmlschema-patterns/
– set of rules – “patterns”
– conforming schemas shall claim best interoperable databinding
– does not constrain the datamodel, e.g. primitive type representation
§ Advanced XML Schema Patterns for Databinding ~220
– these are known to *not* be well supported by some databinding
frameworks/tools
– http://www.w3.org/2002/ws/databinding/edcopy/advanced/advanced.html

W3C – Examples
<xs:schema />
<xs:schema elementFormDefault=“qualified”/>
@XmlSchema(elementFormDefault=XmlNsForm.QUALIFIED)
package mypkg;
<xs:schema elementFormDefault=“unqualified”/>
@XmlSchema(elementFormDefault=XmlNsForm.UNQUALIFIED)
package mypkg;

W3C – Examples
<xs:schema />
<xs:schema attributeFormDefault=“unqualified”/>
@XmlSchema(attributeFormDefault=XmlNsForm.UNQUALIFIED)
package mypkg;
<xs:schema attributeFormDefault=“qualified”/>
@XmlSchema(attributeFormDefault=XmlNsForm.QUALIFIED)
package mypkg;

W3C – Examples
<xs:annotation>
<xs:documentation>State Name</xs:documentation>
</xs:annotation>
<xs:annotation>
<xs:documentation>State Name</xs:documentation>
<xs:appinfo>Application Information</xs:appinfo>
</xs:annotation>

W3C – Examples
§ id=“1”
§ import/include rules
§ <xs:element name=“globalEl” type=“xs:string”>
§ abstract==“false”
§ …
§ <xs:element name="non-Identifier-Name“>
§ abstract==“true”
§ minOccurs / maxOccurs
§ …

Databinding interoperability
§ Framework Language Passed Skip Fail
– A Java 401 185 77
– B Java 455 71 77
– C Java 531 0 72
– D C# 483 61 59
– E Ruby 262 23 318
– F Python 211 89 303
– G C 548 1 54
– H PHP 467 71 65
– I C++ 465 38 100
– J Java 448 33 122
– K Java 499 58 46
– …
(source: http://www.w3.org/2002/ws/databinding/edcopy/report/basic.html)

Common-Sense Approach

Common-Sense Approach
(JAXB view)

Common Sense Alternative
§ No long list of patterns to keep in mind or check against
§ Keep It Short & Simple
§ Works both ways
– Java à Schema
– Schema à Java
– Project based decision

Avoid problematic primitive types
anySimpleType
float decimal double
integer
long nonPositiveInteger nonNegativeInteger
negativeInteger int unsignedLong positiveInteger
short unsignedInt
byte unsignedShort
unsignedByte
§ Boolean / boolean
§ Byte / byte
§ Short / short
§ Integer / int
§ Long / long
§ Double / double
§ BigInteger*

.NET Mapping
§ System.Boolean
§ System.SByte
§ System.Int16
§ System.Int32
§ System.Int64
§ System.Double
§ System.UInt64*
anySimpleType
float decimal double
integer
long nonPositiveInteger nonNegativeInteger
negativeInteger int unsignedLong positiveInteger
short unsignedInt
byte unsignedShort
unsignedByte

Be Explicit. Use @XmlSchemaType
@XmlElement
@XmlSchemaType(name=“xs:long”)
public Long lng;
@XmlElement
@XmlSchemaType(name=“xs:anyUri”)
public java.net.URI uri;

Dates
java.xml.datatype.XmlGregorianCalendar
.NET: String
Java: public XmlGregorianCalendar orderDate;
XSD:<xs:element name=“orderDate” type=“xs:anySimpleType”/>
java.util.Date
java.util.Calendar

Be Explicit
§ If direct date mapping required, still use XmlGregorianCalendar
@XmlSchemaType(name=“dateTime”)
public XMLGregorianCalendar orderDate;
§ XSD: <xs:element name=“orderDate” type=“xs:dateTime”/>
§ .NET: System.DateTime

Avoid Anonymous types
<xsd:complexType name="PurchaseOrderType">
<xs:element name=“…” type=“ns:SomeOtherType”/>
@XmlType()
@XmlType(name=“SomeOtherType”)
<xsd:complexType name="PurchaseOrderType">
…
<xsd:complexType> …
@XmlType(name=“”)

Avoid Mixed Content of Any Type
<ex:notMixed>
<ex:notMixedElement>Stuff</ex:notMixedElement>
</ex:notMixed>
<ex:mixed>
<ex:element1>string</ex:element1>mixed content
<ex:element2>string</ex:element2>
mixed content
</ex:mixed>
@XmlMixed

Avoid Mixed Content of Any Type
@XmlElement(name = “var1")
protected short var1;
@XmlElement(name = “var2")
protected double var2;
…
@XmlElementRefs({
@XmlElementRef(name = “var1", type = JAXBElement.class),
@XmlElementRef(name = “var2", type = JAXBElement.class),
})
@XmlMixed
protected List<Serializable> content;

Avoid substitution groups
<element name="global" type="string"
<element name="global-1" type="string" substitutionGroup="tns:global"/>
<element name="global-2" type="string" substitutionGroup="tns:global"/>

Don’t Rely on Type Inheritance – by restriction
<xs:complexType name=“parentType">
<xs:sequence>
<xs:element name=“e1" type="xs:integer" minOccurs="0" maxOccurs="1"/>
<xs:element name=“e2" type="xs:string" nillable="true" />
</xs:sequence>
<xs:attribute name=“a1" type="xs:date" use="optional" />
</xs:complexType>
<xs:complexType name=“childType"><xs:complexContent>
<xs:restriction base=“parentType">
<xs:sequence>
<xs:element name=“e1" type="xs:integer" minOccurs="1" />
<xs:element name=“e2" type="xs:string" nillable="false" />
</xs:sequence>
<xs:attribute name=“a1" type="xs:date" use="required" />
</xs:restriction>
</xs:complexContent></xs:complexType>

§ Think about datatypes
§ Be explicit
§ Use XMLGregorianCalendar
§ Avoid anonymous types
§ Avoid mixed content!
§ Avoid substitution groups
§ Do not rely on inheritance by restriction

KEEP IT

KEEP IT
SIMPLE

§ http://jaxb.java.net
§ http://blogs.oracle.com/mgrebac
§ http://download.oracle.com/docs/cd/E17802_01/webservices/webservices/reference/
tutorials/wsit/doc/WSITTutorial.pdf
§ http://www.w3.org/TR/xmlschema-patterns/
§ http://www.w3.org/2002/ws/databinding/edcopy/advanced/advanced.html
§ http://www.w3.org/2002/ws/databinding/patterns/6/09/
§ http://msdn.microsoft.com/en-us/library/ff842400%28d=printer%29.aspx
§ http://www.infoq.com/articles/schema-for-ws-part1
§ http://msdn.microsoft.com/en-us/netframework/gg413252
§ http://www.ibm.com/developerworks/xml/library/ws-tip-j2eenet2/index.html
§ http://www.ibm.com/developerworks/java/library/ws-tip-j2eenet3/index.html

Q
&
A

The preceding is intended to outline our general product direction. It is intended
for information purposes only, and may not be incorporated into any contract.
It is not a commitment to deliver any material, code, or functionality, and should
not be relied upon in making purchasing decisions. The development, release,
and timing of any features or functionality described for Oracle’s products
remains at the sole discretion of Oracle.

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