XML Tools Leonidas Fegaras 1

Transcript XML Tools Leonidas Fegaras 1

CSE 6331 © Leonidas Fegaras XML Tools

XML Tools

Leonidas Fegaras 1

XML Processing

Well-formedness checks & reference expansion document XML document parser XML infoset document validator XML infoset (annotated) application DTD or XML schema storage system CSE 6331 © Leonidas Fegaras XML Tools 2

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 CSE 6331 © Leonidas Fegaras XML Tools 3

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 NodeList getElementsByTagName ( String name ); } public interface Document extends Node { public Element getDocumentElement (); } public interface NodeList { public int getLength (); public Node item ( int index ); } CSE 6331 © Leonidas Fegaras XML Tools 4

Traversing the DOM Tree

• Finding all children of node n with a given tagname NodeList nl = n.getChildNodes(); for (int i=0; i

DOM Example

import java.io.File; import javax.xml.parsers.*; import org.w3c.dom.*; /*[dept=“cse”]/tel/text() class Test { public static void main ( String args[] ) throws Exception { DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); Document doc = db.parse(new File("depts.xml")); NodeList nodes = doc.getDocumentElement().getChildNodes(); for (int i=0; i

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; i

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 CSE 6331 © Leonidas Fegaras XML Tools 8

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 ) CSE 6331 © Leonidas Fegaras XML Tools 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(“<” + tag + “>”); } public void endElement ( String uri, String name, String tag ) { System.out.print(“”); } public void characters ( char text[], int start, int length ) { System.out.print(new String(text,start,length)); } } CSE 6331 © Leonidas Fegaras XML Tools 10

The Child Handler

class Child extends DefaultHandler { DefaultHandler next;

// the next handler in the pipeline

String ptag;

// the tagname of the child

boolean keep; short level;

// are we keeping or skipping events?

// 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(); } CSE 6331 © Leonidas Fegaras XML Tools 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); } CSE 6331 © Leonidas Fegaras XML Tools 12

Forming the Pipeline

class SAX { public static void main ( String args[] ) throws Exception { SAXParserFactory pf = SAXParserFactory.newInstance(); SAXParser parser = pf.newSAXParser(); DefaultHandler handler = new Child("gradstudent", new Child("name", new Printer())); parser.parse(new InputSource(new FileReader("cs.xml")), handler); } } SAX parser Child:gradstudent Child:name Printer CSE 6331 © Leonidas Fegaras XML Tools 13

Input Stream

Computer Science

SAX Events

SD: SE: department SE: deptname C: Computer Science EE: deptname SE: gradstudent SE: name Smith John SE: lastname C: Smith EE: lastname SE: firstname C: John EE: firstname EE: name EE: gradstudent ...

...

EE: department ED: CSE 6331 © Leonidas Fegaras XML Tools

Example

Child: gradstudent Child: name Printer

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/ CSE 6331 © Leonidas Fegaras XML Tools 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 {} CSE 6331 © Leonidas Fegaras XML Tools 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; } CSE 6331 © Leonidas Fegaras XML Tools 17

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 String[len]; String[] values = new String[len]; for (int i = 0; i

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 > 0) { state++; if (state == 2) return new EOS(); }; Event e = getEvent(); if (xpp.getEventType() != XmlPullParser.END_DOCUMENT) xpp.next(); return e; } CSE 6331 © Leonidas Fegaras XML Tools 19

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; return t; }; if (keep) return t; } } } CSE 6331 © Leonidas Fegaras XML Tools 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: CSE 6331 © Leonidas Fegaras XML Tools 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: … The default (implicit) templates visit all nodes and strip out all tags: CSE 6331 © Leonidas Fegaras XML Tools 22

Other XSLT Elements

select the value of an XML element and add it to the output stream of the transformation, e.g. .

copy the entire XML element to the output stream of the transformation.

apply the template rules to the elements that match the XPath expression.

… add an element to the output with a tag-name derived from the XPath.

Copy the Entire Document

More on XSLT

•

Conflict resolution

: more specific templates overwrite more general templates. Templates are assigned default priorities, but they can be overwritten using priority=“n” in a template.

• Modes can be used to group together templates. No mode is an empty mode.

• Conditional and loop statements: body body • Variables can be used to name data: value Variables are used as {$x} in XPaths.

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 = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); Document document = db.parse(xmlfile); StreamSource stylesource = new StreamSource(stylesheet); TransformerFactory tf = TransformerFactory.newInstance(); Transformer transformer = tf.newTransformer(stylesource); DOMSource source = new DOMSource(document); StreamResult result = new StreamResult(System.out); transformer.transform(source,result); } } CSE 6331 © Leonidas Fegaras XML Tools 26