XML Tools

1
XML Tools

• Leonidas Fegaras

2
XML Processing
Well-formedness checks reference expansion
document parser
document validator
application
XML infoset
XML infoset (annotated)
XML document
DTD or XML schema
storage system
3
Tools for XML Processing

• DOM a language-neutral interface for
  manipulating XML data
• requires that the entire document be in memory
• SAX push-based stream processing
• hard to write non-trivial applications
• XPath a declarative tree-navigation language
• beautiful and easy to use
• is part of many other languages
• XSLT a language for transforming XML based on
  templates
• very ugly!
• XQuery full-fledged query language
• influenced by OQL
• XmlPull pull-based stream processing
• far better than SAX, but not a standard yet

4
DOM

• The Document Object Model (DOM) is a platform-
  and language-neutral interface that allows
  programs and scripts to dynamically access and
  update the content and structure of XML
  documents.
• The following is part of the DOM interface
• public interface Node
• public String getNodeName ()
• public String getNodeValue ()
• public NodeList getChildNodes ()
• public NamedNodeMap getAttributes ()
• public interface Element extends Node
• public Node getElementsByTagName ( String name
  )
• public interface Document extends Node
• public Element getDocumentElement ()
• public interface NodeList
• public int getLength ()
• public Node item ( int index )

5
DOM Example

• import java.io.File
• import javax.xml.parsers.
• import org.w3c.dom.
• class Test
• public static void main ( String args ) throws
  Exception
• DocumentBuilderFactory dbf DocumentBuilderFacto
  ry.newInstance()
• DocumentBuilder db dbf.newDocumentBuilder()
• Document doc db.parse(new File("depts.xml"))
• NodeList nodes doc.getDocumentElement().getChil
  dNodes()
• for (int i0 iltnodes.getLength() i)
• Node n nodes.item(i)
• NodeList ndl n.getChildNodes()
• for (int k0 kltndl.getLength() k)
• Node m ndl.item(k)
• if ( (m.getNodeName() "dept")
• (m.getFirstChild().getNodeValue() "cse")
  )
• NodeList ncl ((Element)
  m).getElementsByTagName("tel")
• for (int j0 jltncl.getLength() j)

/dept/text()cse/tel/text()
6
Better Programming

• import java.io.File
• import javax.xml.parsers.
• import org.w3c.dom.
• import java.util.Vector
• class Sequence extends Vector
• Sequence () super()
• Sequence ( String filename ) throws Exception
  
• super()
• DocumentBuilderFactory dbf
• DocumentBuilderFactory.newInstance()
• DocumentBuilder db dbf.newDocumentBuilder()
• Document doc db.parse(new File(filename))
• add((Object) doc.getDocumentElement())

Sequence child ( String tagname )
Sequence result new Sequence() for
(int i 0 iltsize() i) Node n
(Node) elementAt(i) NodeList c
n.getChildNodes() for (int k 0
kltc.getLength() k) if (c.item(k).getNodeName(
).equals(tagname)) result.add((Object)
c.item(k)) return result
void print () for (int i 0
iltsize() i) System.out.println(e
lementAt(i).toString())
class DOM public static void main ( String
args ) throws Exception (new
Sequence("cs.xml")).child("gradstudent").child("na
me").print()
7
SAX

• SAX is a Simple API for XML that allows you to
  process a document as it's being read
• in contrast to DOM, which requires the entire
  document to be read before it takes any action)
• The SAX API is event based
• The XML parser sends events, such as the start or
  the end of an element, to an event handler, which
  processes the information

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Parser Events

• Receive notification of the beginning of a
  document
• void startDocument ()
• Receive notification of the end of a document
• void endDocument ()
• Receive notification of the beginning of an
  element
• void startElement ( String namespace, String
  localName,
• String qName, Attributes atts )
• Receive notification of the end of an element
• void endElement ( String namespace, String
  localName,
• String qName )
• Receive notification of character data
• void characters ( char ch, int start, int
  length )

9
SAX Example a Printer

• import java.io.FileReader
• import javax.xml.parsers.
• import org.xml.sax.
• import org.xml.sax.helpers.
• class Printer extends DefaultHandler
• public Printer () super()
• public void startDocument ()
• public void endDocument () System.out.println(
  )
• public void startElement ( String uri, String
  name,
• String tag, Attributes atts )
• System.out.print(lt tag gt)
• public void endElement ( String uri, String
  name, String tag )
• System.out.print(lt/ tag gt)
• public void characters ( char text, int
  start, int length )
• System.out.print(new String(text,start,lengt
  h))

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The Child Handler

• class Child extends DefaultHandler
• DefaultHandler next // the next handler in
  the pipeline
• String ptag // the tagname of the child
• boolean keep // are we keeping or skipping
  events?
• short level // the depth level of the
  current element
• public Child ( String s, DefaultHandler n )
• super()
• next n ptag s
• keep false level 0
• public void startDocument () throws
  SAXException
• next.startDocument()
• public void endDocument () throws
  SAXException
• next.endDocument()

11
The Child Handler (cont.)

• public void startElement ( String nm, String
  ln, String qn, Attributes a ) throws SAXException
  
• if (level 1)
• keep ptag.equals(qn)
• if (keep)
• next.startElement(nm,ln,qn,a)
• public void endElement ( String nm, String
  ln, String qn ) throws SAXException
• if (keep)
• next.endElement(nm,ln,qn)
• if (--level 1)
• keep false
• public void characters ( char text, int
  start, int length ) throws SAXException
• if (keep)
• next.characters(text,start,length)

12
Forming the Pipeline

• class SAX
• public static void main ( String args )
  throws Exception
• SAXParserFactory pf SAXParserFactory.new
  Instance()
• SAXParser parser pf.newSAXParser()
• DefaultHandler handler
• new Child("gradstudent",
• new Child("name",
• new Printer()))
• parser.parse(new InputSource(new
  FileReader("cs.xml")),
• handler)

Childname
Printer
SAX parser
Childgradstudent
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Example

• Input Stream
• ltdepartmentgt
• ltdeptnamegt
• Computer Science
• lt/deptnamegt
• ltgradstudentgt
• ltnamegt
• ltlastnamegt
• Smith
• lt/lastnamegt
• ltfirstnamegt
• John
• lt/firstnamegt
• lt/namegt
• lt/gradstudentgt
• ...
• lt/departmentgt

SAX Events SD SE department SE deptname C
Computer Science EE deptname SE gradstudent SE
name SE lastname C Smith EE lastname SE
firstname C John EE firstname EE name EE
gradstudent ... EE department ED
Child gradstudent
Child name
Printer
14
XmlPull

• Unlike SAX, you pull events from document
• Create a pull parser
• XmlPullParser xpp
• xpp factory.newPullParser()
• Pull the next event xpp.getEventType()
• Type of events
• START_TAG
• END_TAG
• TEXT
• START_DOCUMENT
• END_DOCUMENT
• More information at
• http//www.xmlpull.org/

15
Better XmlPull Events

• class Attributes
• public String names
• public String values
• abstract class Event
• class StartTag extends Event
• public String tag
• public Attributes attributes
• class EndTag extends Event
• public String tag
• class CData extends Event
• public String text
• class EOS extends Event

16
Iterators

• import org.xmlpull.v1.XmlPullParser
• import org.xmlpull.v1.XmlPullParserFactory
• abstract class Iterator
• abstract public void open () // open the
  stream iterator
• abstract public void close () // close the
  stream iterator
• abstract public Event next () // get the
  next tuple from stream
• abstract class Filter extends Iterator
• Iterator input

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Document Reader

• class Document extends Iterator
• String path
• int state
• FileReader reader
• XmlPullParser xpp
• static XmlPullParserFactory factory
• Event getEvent ()
• int eventType xpp.getEventType()
• if (eventType XmlPullParser.START_TAG)
• int len xpp.getAttributeCount()
• String names new Stringlen
• String values new Stringlen
• for (int i 0 iltlen i)
• namesi xpp.getAttributeName(i)
• valuesi xpp.getAttributeValue(i)
• return new StartTag(xpp.getName(),new
  Attributes(names,values))
• else if (eventType XmlPullParser.END_TAG
  )
• return new EndTag(xpp.getName())

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Document Reader (cont.)

• public void open ()
• reader new FileReader(path)
• xpp factory.newPullParser()
• xpp.setInput(reader)
• state 0
• public void close ()
• reader.close()
• public Event next ()
• if (state gt 0)
• state
• if (state 2)
• return new EOS()
• Event e getEvent()
• if (xpp.getEventType() ! XmlPullParser.END_DOCUM
  ENT)
• xpp.next()
• return e

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The Child Iterator

• class Child extends Filter
• String tag
• short nest // the nesting level of the
  event
• boolean keep // are we in keeping mode?
• public void open () keep false nest 0
  input.open()
• public Event next ()
• while (true)
• Event t input.next()
• if (t instanceof EOS)
• return t
• else if (t instanceof StartTag)
• if (nest 1)
• keep tag.equals(((StartTag) t).tag)
• if (!keep)
• continue
• else if (t instanceof EndTag)
• if (--nest 1 keep)
• keep false

20
XSL Transformation

• A stylesheet specification language for
  converting XML documents into various forms (XML,
  HTML, plain text, etc).
• Can transform each XML element into another
  element, add new elements into the output file,
  or remove elements.
• Can rearrange and sort elements, test and make
  decisions about which elements to display, and
  much more.
• Based on XPath
• ltxslstylesheet version1.0
• xmlnsxslhttp//www.w3.org/1999/XSL/Transform
  gt
• ltstudentsgt
• ltxslcopy-of select//student/name/gt
• lt/studentsgt
• lt/xslstylesheetgt

21
XSLT Templates

• XSL uses XPath to define parts of the source
  document that match one or more predefined
  templates.
• When a match is found, XSLT will transform the
  matching part of the source document into the
  result document.
• The parts of the source document that do not
  match a template will end up unmodified in the
  result document (they will use the default
  templates).
• Form
• ltxsltemplate matchXPath expressiongt
• lt/xsltemplategt
• The default (implicit) templates visit all nodes
  and strip out all tags
• ltxsltemplate match/gt
• ltxslapply-templates/gt
• lt/xsltemplategt
• ltxsltemplate matchtext()_at_"gt
• ltxslvalue-of select./gt
• lt/xsltemplategt

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Other XSLT Elements

• ltxslvalue-of selectXPath expression/gt
• select the value of an XML element and add it to
  the output stream of the transformation, e.g.
  ltxslvalue-of select"//books/book/author"/gt.
• ltxslcopy-of selectXPath expression/gt
• copy the entire XML element to the output stream
  of the transformation.
• ltxslapply-templates matchXPath expression/gt
• apply the template rules to the elements that
  match the XPath expression.
• ltxslelement nameXPath expressiongt
  lt/xslelementgt
• add an element to the output with a tag-name
  derived from the XPath.
• Example
• ltxslstylesheet version 1.0
• xmlnsxslhttp//www.w3.org/1999/XSL/Tra
  nsformgt
• ltxsltemplate match"employee"gt
• ltbgt ltxslapply-templates select"node()"/gt
  lt/bgt
• lt/xsltemplategt
• ltxsltemplate match"surname"gt
• ltigt ltxslvalue-of select"."/gt lt/igt
• lt/xsltemplategt
• lt/xslstylesheetgt

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Copy the Entire Document

• ltxslstylesheet version 1.0
• xmlnsxslhttp//www.w3.org/1999/XSL/Transfo
  rmgt
• ltxsltemplate match/"gt
• ltxslapply-templates/gt
• lt/xsltemplategt
• ltxsltemplate matchtext()"gt
• ltxslvalue-of select./gt
• lt/xsltemplategt
• ltxsltemplate match"gt
• ltxslelement namename(.)gt
• ltxslapply-templates/gt
• lt/xslelementgt
• lt/xsltemplategt
• lt/xslstylesheetgt

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More on XSLT

• Conflict resolution more specific templates
  overwrite more general templates. Templates are
  assigned default priorities, but they can be
  overwritten using priorityn in a template.
• Modes can be used to group together templates. No
  mode is an empty mode.
• ltxsltemplate match modeAgt
• ltxslapply-templates modeB/gt
• lt/xsltemplategt
• Conditional and loop statements
• ltxslif testXPath predicategt body lt/xslifgt
• ltxslfor-each selectXPathgt body
  lt/xslfor-eachgt
• Variables can be used to name data
• ltxslvariable namexgt value lt/xslvariablegt
• Variables are used as x in XPaths.

25
Using XSLT

• import javax.xml.parsers.
• import org.xml.sax.
• import org.w3c.dom.
• import javax.xml.transform.
• import javax.xml. . transform.dom.
• import javax.xml.transformstream.
• import java.io.
• class XSLT
• public static void main ( String argv )
  throws Exception
• File stylesheet new File("x.xsl")
• File xmlfile new File("a.xml")
• DocumentBuilderFactory dbf DocumentBuilderFacto
  ry.newInstance()
• DocumentBuilder db dbf.newDocumentBuilder()
• Document document db.parse(xmlfile)
• StreamSource stylesource new
  StreamSource(stylesheet)
• TransformerFactory tf TransformerFactory.newIns
  tance()
• Transformer transformer tf.newTransformer(style
  source)
• DOMSource source new DOMSource(document)