JAXB

1. JAXB Java Architecture for XML Bindings

2. 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/webservices/downloads/webservicespack.html

3. 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!

4. High-level comparison • Before diving into details of JAXB, it’s good to see a bird’s-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

5. 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

6. Running binding compiler • <install_dir>/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. We’ll study them only at a high level so we can understand how to use them

7. Example: students.xsd

8. 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 <students> • test/lottery/StudentsType.java • Represents the unnamed type of each student object

9. 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

10. 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

11. 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.

12. Sample Programs

13. 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

14. 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!

15. Some additional JAXB details

16. 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

17. 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 "xsd:NCName" 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. • Bind model group with a repeating occurrence and complex type definitions with mixed {content type} to: • A general content property; a List content-property that holds Java instances representing element information items and character data items.