JAXB

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JAXB

• Java Architecture for XML Bindings

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What is JAXB?

• JAXB defines the behavior of a standard set of
  tools and interfaces that automatically generate
  java class files from XML schema
• JAXB is a framework or architecture, not an
  implementation.
• Sun provides a reference implementation of JAXB
  with the Web Services Developers kit, available
  as a separate download http//java.sun.com/webserv
  ices/downloads/webservicespack.html

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JAXB vs. DOM and SAX

• JAXB is a higher level construct than DOM or SAX
• DOM represents XML documents as generic trees
• SAX represents XML documents as generic event
  streams
• JAXB represents XML documents as Java classes
  with properties that are specific to the
  particular XML document
• E.g. book.xml becomes Book.java with getTitle,
  setTitle, etc.
• JAXB thus requires almost no knowledge of XML to
  be able to programmatically process XML documents!

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High-level comparison

• Before diving into details of JAXB, its good to
  see a birds-eye-view of the difference between
  JAXB and SAX and/or DOM-like parsers
• Study the books/ examples under the examples/jaxb
  directory on the course website

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JAXB steps

• We start by assuming that you have a valid
  installation of java web services developers pack
  version 3. We cover these installation details
  later
• Using JAXB then requires several steps
• Run the binding compiler on the schema file to
  automagically produce the appropriate java class
  files
• Compile the java class files (ant tool helps
  here)
• Study the autogenerated api to learn what java
  types have been created
• Create a program that unmarshals an xml document
  into these elementary data structures

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Running binding compiler

• ltinstall_dirgt/jaxb/bin/xjc.sh -p test.jaxb
  books.xsd -d work
• xjc.sh executes binding compiler
• -p test.jaxb place resulting class files in
  package test.jaxb
• books.xsd run compiler on schema books.xsd
• -d work place resulting files in directory
  called work/
• Note that this creates a huge number of files
  that together represent the content of the
  books.xsd schema as a set of Java classes
• It is not necessary to know all of these classes.
  Well study them only at a high level so we can
  understand how to use them

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Example students.xsd
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Generated interfaces

• xjc.sh -p test.lottery students.xsd
• This generates the following interfaces
• test/lottery/ObjectFactory.java
• Contains methods for generating instances of the
  interfaces
• test/lottery/Students.java
• Represents the root node ltstudentsgt
• test/lottery/StudentsType.java
• Represents the unnamed type of each student object

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Generated implementations

• Each interface is implemented in the impl
  directory
• test/lottery/impl/StudentsImpl.java
• Vendor-specific implementation of the Students
  inteface
• test/lottery/impl/StudentsTypeImpl.java
• Vendor-specific implementation of the
  StudentsType Interface

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Compilation

• Next, the generated classes must be compiled
• javac students/.java students/impl/.java
• CLASSPATH requires many jar files
• jaxb/lib/.jar
• jwsdp-shared/lib/.jar
• jaxp/lib//.jar
• Note an ant buildfile (like a java makefile)
  makes this much easier. More on this later

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Generated docs

• Java API docs for these classes are generated in
• students/docs/api/.html
• After bindings are generated, one usually works
  directly through these API docs to learn how to
  access/manipulate the XML data.

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Sample Programs
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Sample Programs

• Easiest way to learn is to cover certain generic
  sample cases. These are all on the course website
  under cspp53025/examples/jaxb
• Summary of examples
• student/
• Use JAXB to read an xml document composed of a
  single student complex type
• student/
• Same, but for an xml document composed of a
  sequence of such student types of indefinite
  length
• purchaseOrder/
• Another read example, but for a more complex
  schema

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Sample programs, cont

• Course examples, cont
• create-marshal
• Purchase-order example modified to create in
  memory and write to XML
• modify-marshal
• Purchase-order example modified to read XML,
  change it and write back to XML
• Study these examples!

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Some additional JAXB details
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Binding Data Types

• Default java datatype bindings can be found at
• http//java.sun.com/webservices/docs/1.3/tutorial/
  doc/JAXBWorks5.html
• These defaults can be changed if required for an
  application
• Also, name binding are fairly standard changes of
  names to things acceptable in java programming
  language
• See other binding rules on subsequent pages

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Default binding rules summary

• The JAXB binding model follows the default
  binding rules summarized below
• Bind the following to Java package
• XML Namespace URI
• Bind the following XML Schema components to Java
  content interface
• Named complex type
• Anonymous inlined type definition of an element
  declaration
• Bind to typesafe enum class
• A named simple type definition with a basetype
  that derives from "xsdNCName" and has
  enumeration facets.
• Bind the following XML Schema components to a
  Java Element interface
• A global element declaration to a Element
  interface.
• Local element declaration that can be inserted
  into a general content list.
• Bind to Java property
• Attribute use
• Particle with a term that is an element reference
  or local element declaration.