1. XML: eXtensible Markup Language
Creating portable data

2. Java E-Commerce © Martin Cooke, 2003
Plan
DOM & SAX
Processing XML in Java
Transforming XML with XSL
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3. Java E-Commerce © Martin Cooke, 2003
Reminder: XML example
<?xml version="1.0" encoding="UTF-8"?>
<Curriculum>
<Course Title="Z" Lect="Bogdanov">
<Lecture>Props</Lecture>
<Lecture>Predicates</Lecture>
<Lecture>Sets</Lecture>
</Course>
</Curriculum>
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4. SAX & DOM

5. Document object model (DOM)
A means of representing an XML document within a program
Not tied to Java: cross-language, cross-platform
Programmers use DOM through APIs
Parsing XML results in a DOM tree
Tree can be traversed, searched, mutated, output
Loads entire document into memory
slow
hungry
DOM
read/write model (can generate XML doc or modify XML doc)
creates model of document in memory for later use
slower
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6. Simple API for XML (SAX)
Another way to process XML
Incremental parsing
Works via parser callbacks
Programmer registers handlers with parser
As XML is being parsed, these handlers are called
Does not allow random access to XML doc
Fast and efficient
Not mutable (unless you build a copy)
Good model for transformations (see later)
SAX
read-only model
event-based
e.g. when a new <ELEMENT> is read in, a method is called to process it
fast
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7. The view from Java

8. Java E-Commerce © Martin Cooke, 2003
JDOM
Java-centric, high-performance alternative to DOM & SAX
Far simpler in use
Provides high performance of SAX
Rapid parsing and output
Provides document model of DOM without memory problems
Mutable, random-access
Integrated with Java Collections framework:
Methods return List, Map etc
JDOM
all the benefits of DOM but fast
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Parsing XML with JDOM
// Get a document builder
SAXBuilder builder = new SAXBuilder();
// use it to read/parse an XML document
Document doc = builder.build(new File(args[0]));
// get and print the root element
Element root = doc.getRootElement();
System.out.println("Root is " + root);
// now get children whose name matches "Course"
List children = root.getChildren("Course");
Iterator i = children.iterator();
while (i.hasNext()) {
Element child = (Element) i.next();
System.out.println(" --> "+child); }
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Parsing XML with JDOM
SaxBuilder implements the Builder interface, which mandates several build methods, from
InputStream
File
URL
Can also use DOMBuilder (slower)
Builder pattern allows client to contruct a complex object by specifying its type and content, and without having to worry about the internals
// Get a document builder
SAXBuilder builder = new SAXBuilder();
// use it to read/parse an XML document
Document doc = builder.build(new File(args[0]));
// get and print the root element
Element root = doc.getRootElement();
System.out.println("Root is " + root);
// now get children whose name matches "Course"
List children = root.getChildren("Course");
Iterator i = children.iterator();
while (i.hasNext()) {
Element child = (Element) i.next();
System.out.println(" --> "+child); }
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Parsing XML with JDOM
// Get a document builder
SAXBuilder builder = new SAXBuilder();
// use it to read/parse an XML document
Document doc = builder.build(new File(args[0]));
// get and print the root element
Element root = doc.getRootElement();
System.out.println("Root is " + root);
// now get children whose name matches "Course"
List children = root.getChildren("Course");
Iterator i = children.iterator();
while (i.hasNext()) {
Element child = (Element) i.next();
System.out.println(" --> "+child); }
Element is fundamental class in JDOM
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12. Java E-Commerce © Martin Cooke, 2003
Parsing XML with JDOM
// Get a document builder
SAXBuilder builder = new SAXBuilder();
// use it to read/parse an XML document
Document doc = builder.build(new File(args[0]));
// get and print the root element
Element root = doc.getRootElement();
System.out.println("Root is " + root);
// now get children whose name matches "Course"
List children = root.getChildren("Course");
Iterator i = children.iterator();
while (i.hasNext()) {
Element child = (Element) i.next();
System.out.println(" --> "+child); }
Many JDOM methods return Collection objects such as List
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13. Parsing XML with DTD validation
// Get a document builder
SAXBuilder builder = new SAXBuilder(true);
// use it to read/parse an XML document
Document doc = builder.build(new File(args[0]));
// get and print the root element
Element root = doc.getRootElement();
System.out.println("Root is " + root);
// now get children whose name matches "Course"
List children = root.getChildren("Course");
Iterator i = children.iterator();
while (i.hasNext()) {
Element child = (Element) i.next();
System.out.println(" --> "+child); }
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Output
// Get a document builder
SAXBuilder builder = new SAXBuilder();
// use it to read/parse an XML document
Document doc = builder.build(new File(args[0]));
// get and print the root element
Element root = doc.getRootElement();
System.out.println("Root is " + root);
// now get children whose name matches "Course"
List children = root.getChildren("Course");
Iterator i = children.iterator();
while (i.hasNext()) {
Element child = (Element) i.next();
System.out.println(" --> "+child); }
Root is [Element: <Curriculum />]
--> [Element: <Course />]
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15. Java E-Commerce © Martin Cooke, 2003
Generating XML
Element curriculum = new Element("Curriculum");
Document doc = new Document(curriculum);
Element course = new Element("Course");
course.addAttribute("Title","Java");
course.addAttribute("Lect","Brown");
Element lecture1 = new Element("Lecture"). setText("Overview");
Element lecture2 = new Element("Lecture"). setText("Basics");
course.addContent(lecture1);
course.addContent(lecture2);
curriculum.addContent(course);
XMLOutputter out = new XMLOutputter(" ",true);
out.output(doc,System.out);
Creating a new XML document is simply a matter of generating a root element
Note that this omits the try catch
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16. Java E-Commerce © Martin Cooke, 2003
Generating XML
Element curriculum = new Element("Curriculum");
Document doc = new Document(curriculum);
Element course = new Element("Course");
course.addAttribute("Title","Java");
course.addAttribute("Lect","Brown");
Element lecture1 = new Element("Lecture"). setText("Overview");
Element lecture2 = new Element("Lecture"). setText("Basics");
course.addContent(lecture1);
course.addContent(lecture2);
curriculum.addContent(course);
XMLOutputter out = new XMLOutputter(" ",true);
out.output(doc,System.out);
Similarly, straightforward to produce elements with attributes
Note that this omits the try catch
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17. Java E-Commerce © Martin Cooke, 2003
Generating XML
Element curriculum = new Element("Curriculum");
Document doc = new Document(curriculum);
Element course = new Element("Course");
course.addAttribute("Title","Java");
course.addAttribute("Lect","Brown");
Element lecture1 = new Element("Lecture"). setText("Overview");
Element lecture2 = new Element("Lecture"). setText("Basics");
course.addContent(lecture1);
course.addContent(lecture2);
curriculum.addContent(course);
XMLOutputter out = new XMLOutputter(" ",true);
out.output(doc,System.out);
… add content
Note that this omits the try catch
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Generating XML
Element curriculum = new Element("Curriculum");
Document doc = new Document(curriculum);
Element course = new Element("Course");
course.addAttribute("Title","Java");
course.addAttribute("Lect","Brown");
Element lecture1 = new Element("Lecture"). setText("Overview");
Element lecture2 = new Element("Lecture"). setText("Basics");
course.addContent(lecture1);
course.addContent(lecture2);
curriculum.addContent(course);
XMLOutputter out = new XMLOutputter(" ",true);
out.output(doc,System.out);
… and to output the document
Arguments to XMLOutputter ensure indenting and pretty-printing
Can also output
DOM
SAX events
Note that this omits the try catch
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19. Java E-Commerce © Martin Cooke, 2003
Adding a DTD
Element curriculum = new Element("Curriculum");
Document doc = new Document(curriculum);
doc.setDocType
(new DocType("Curriculum","Curric.DTD"));
Element course = new Element("Course");
course.addAttribute("Title","Java");
course.addAttribute("Lect","Brown");
Element lecture1 = new Element("Lecture"). setText("Overview");
Element lecture2 = new Element("Lecture"). setText("Basics");
course.addContent(lecture1);
course.addContent(lecture2);
curriculum.addContent(course);
XMLOutputter out = new XMLOutputter(" ",true);
out.output(doc,System.out);
Note that this omits the try catch
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20. Java E-Commerce © Martin Cooke, 2003
Nested generation
Source: JDOM slides
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21. Accessing nested elements
Source: JDOM slides
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22. JDOM likely to be part of Java core
Source:
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23. Java E-Commerce © Martin Cooke, 2003
Suggested homework
Download and familiarise yourself with JDOM from jdom.org
Note that this omits the try catch
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24. Transforming XML

25. Java E-Commerce © Martin Cooke, 2003
Motivation
XML is useful in itself as a means of storing and transmitting data of all kinds…
… but it can be made more useful via transformation
Why?
Store in one format, display in another
Deliver same content in different forms (html, pdf, wml, different XML)
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How?
Option 1: DOM manipulation in a programming language such as Java
Gives complete control
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27. Java E-Commerce © Martin Cooke, 2003
How?
Option 1: DOM manipulation in a programming language such as Java
Gives complete control
Option 2: Using stylesheets
Specifically, using the eXtensible Stylesheet Language for Transformations, XSLT
Usually simpler (if you know XSLT), especially for XML-to-XML transformation
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XSLT
XSLT (extensible stylesheet language for transformation)
Subset of XSL, but frequently use XSL to refer to XSLT
Odd at first to consider a transformation as a ‘style’ application
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Basic idea
The transformation takes an input tree and outputs a tree
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE Curriculum SYSTEM "Curric.DTD">
<Curriculum>
<Course Title="Z" Lect="Kyrill Bogdanov">
<Lecture>Propositions</Lecture>
<Lecture>Predicates</Lecture>
<Lecture>Sets</Lecture>
</Course>
<Course Title="UML" Lect="Marian Gheorge">
<Lecture>Use Cases</Lecture>
<Lecture>Class Diagrams</Lecture>
</Curriculum>
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Basic idea
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE Curriculum SYSTEM "Curric.DTD">
<Curriculum>
<Course Title="Z" Lect="Kyrill Bogdanov">
<Lecture>Propositions</Lecture>
<Lecture>Predicates</Lecture>
<Lecture>Sets</Lecture>
</Course>
<Course Title="UML" Lect="Marian Gheorge">
<Lecture>Use Cases</Lecture>
<Lecture>Class Diagrams</Lecture>
</Curriculum>
The transformation consists of a set of transformation rules, each of which focuses on one level of the tree
Each rule
1. Matches node in tree
2. Specifies structure of output
3. Indicates action for child nodes
Finally, the results of all these rule applications are assembled to form the output tree
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31. Java E-Commerce © Martin Cooke, 2003
Example rule
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl=" version="1.0">
<xsl:template match="/">
<html>
<body>
<h1>
A simple transformation
</h1>
</body>
</html>
</xsl:template>
</xsl:stylesheet>
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32. Java E-Commerce © Martin Cooke, 2003
Example rule
The stylesheet is an XML document
ALL content must be well-formed XML (even generated HTML)
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl=" version="1.0">
<xsl:template match="/">
<html>
<body>
<h1>
A simple transformation
</h1>
</body>
</html>
</xsl:template>
</xsl:stylesheet>
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33. Java E-Commerce © Martin Cooke, 2003
Example rule
The stylesheet is an XML document
ALL content must be well-formed XML (even generated HTML)
The xsl namespace allows the processor to distinguish stylesheet infrastructure from the rest
A namespace is an XML concept which prevents naming clashes
It also helps preprocessors to extract certain elements Eg mathML elements
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl=" version="1.0">
<xsl:template match="/">
<html>
<body>
<h1>
A simple transformation
</h1>
</body>
</html>
</xsl:template>
</xsl:stylesheet>
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34. Java E-Commerce © Martin Cooke, 2003
Example rule
Outputs
<html>
<body>
<h1>
A simple transformation
</h1>
</body>
</html>
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl=" version="1.0">
<xsl:template match="/">
<html>
<body>
<h1>
A simple transformation
</h1>
</body>
</html>
</xsl:template>
</xsl:stylesheet>
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Example rule
Outputs
<html>
<body>
<h1>
A simple transformation
</h1>
</body>
</html>
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl=" version="1.0">
<xsl:template match="/">
<html>
<body>
<h1>
A simple transformation
</h1>
</body>
</html>
</xsl:template>
</xsl:stylesheet>
Match attribute selects a level of the input tree: here, the root
No further rules to match, so default is to copy everything
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Apply-templates
<xsl:template match="Curriculum">
<html>
<body>
<h1>Curriculum</h1>
<ul>
<xsl:apply-templates/>
</ul>
</body>
</html>
</xsl:template>
<xsl:template match="Course">
<li> <xsl:value-of
<html>
<body>
<h1>Curriculum</h1>
<ul>
<li>Z</li>
<li>UML</li>
</ul>
</body>
</html>
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37. Java E-Commerce © Martin Cooke, 2003
Apply-templates
<xsl:template match="Curriculum">
<html>
<body>
<h1>Curriculum</h1>
<ul>
<xsl:apply-templates/>
</ul>
</body>
</html>
</xsl:template>
<xsl:template match="Course">
<li> <xsl:value-of
<html>
<body>
<h1>Curriculum</h1>
<ul>
<li>Z</li>
<li>UML</li>
</ul>
</body>
</html>
The apply-templates rule looks for appropriate templates to apply (here, Course)
value-of extracts attribute values
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Loops and numbering
<xsl:template match="Curriculum">
<html>
<body>
<h1>Curriculum</h1>
<xsl:for-each select="Course">
<xsl:number value="position()"/>.
<xsl:value-of
<ul>
<xsl:apply-templates/>
</ul>
</xsl:for-each>
</body>
</html>
</xsl:template>
<xsl:template match="Lecture">
<li><xsl:value-of select="."/></li>
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39. Java E-Commerce © Martin Cooke, 2003
Loops and numbering
<xsl:template match="Curriculum">
<html>
<body>
<h1>Curriculum</h1>
<xsl:for-each select="Course">
<xsl:number value="position()"/>.
<xsl:value-of
<ul>
<xsl:apply-templates/>
</ul>
</xsl:for-each>
</body>
</html>
</xsl:template>
<xsl:template match="Lecture">
<li><xsl:value-of select="."/></li>
Don’t have to use separate templates. Here, Course is matched using select
select=“.” matches the context (current) node
Many built-in functions such as position()
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40. Java E-Commerce © Martin Cooke, 2003
Match patterns
element
Match=“Course”
attribute
alternatives
Match=“Lecture | Tutorial”
absolute
Match=“/*/Course”
Elements in context
Match=“Course/Lecture”
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41. Java E-Commerce © Martin Cooke, 2003
How-to
Download Xalan from Apache
Various options, but simplest for testing is to
add xalan.jar and xerxes.jar to java classpath
from command line:
java org.apache.xalan.xslt.Process -IN foo.xml -XSL foo.xsl -OUT foo.out
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42. Other means of applying XSLT stylesheets
On the client browser (IE5 implements XSLT)
From a servlet (see later), using a Transformer instance
As part of a web publishing framework
eg. Cocoon from Apache
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43. More complex transforms
Some conversions need more support
Eg XML to PDF
Formatting Objects to PDF (FOP)
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44. Java E-Commerce © Martin Cooke, 2003
Summary
Good support in Java for XML
JDOM
Transformation of XML is often most easily accomplished using XSL, but can be done programmatically
Web publishing frameworks exist to simplify document delivery to multiple devices
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45. Resources

46. Java E-Commerce © Martin Cooke, 2003
Books
Ray (2001) Learning XML, O’Reilly,
McLaughlin (2000) Java & XML, O’Reilly,
Check if later version
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Online documents
XML Tutorials for Programmers
(online XML parser -- requires registration)
Transforming XML to PDF
Why XML?
XSL for fun and diversion
Simplify XML programming with JDOM
Easy Java/XML integration with JDOM, Part 1
Tip: Using JDOM and XSLT
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48. Java E-Commerce © Martin Cooke, 2003
Websites
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