CSE 6331 © Leonidas Fegaras XML Tools1 XML Tools Leonidas Fegaras

CSE 6331 © Leonidas Fegaras XML Tools2 XML Processing document parser document validator application XML document XML infoset XML infoset (annotated) Well-formedness checks & reference expansion DTD or XML schema storage system

CSE 6331 © Leonidas Fegaras XML Tools3 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 Tools4 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 ); }

CSE 6331 © Leonidas Fegaras XML Tools5 import java.io.File; import javax.xml.parsers.*; import org.w3c.dom.*; 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<nodes.getLength(); i++) { Node n = nodes.item(i); NodeList ndl = n.getChildNodes(); for (int k=0; k<ndl.getLength(); k++) { Node m = ndl.item(k); if ( (m.getNodeName() == "dept") && (m.getFirstChild().getNodeValue() == "cse") ) { NodeList ncl = ((Element) m).getElementsByTagName("tel"); for (int j=0; j<ncl.getLength(); j++) { Node nc = ncl.item(j); System.out.print(nc.getFirstChild().getNodeValue()); } } } DOM Example /*[dept/text()=“cse”]/tel/text()

CSE 6331 © Leonidas Fegaras XML Tools6 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<size(); i++) { Node n = (Node) elementAt(i); NodeList c = n.getChildNodes(); for (int k = 0; k<c.getLength(); k++) if (c.item(k).getNodeName().equals(tagname)) result.add((Object) c.item(k)); }; return result; } void print () { for (int i = 0; i<size(); i++) System.out.println(elementAt(i).toString()); } class DOM { public static void main ( String args[] ) throws Exception { (new Sequence("cs.xml")).child("gradstudent").child("name").print(); }

CSE 6331 © Leonidas Fegaras XML Tools7 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 Tools8 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 Tools9 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(“ ”); } 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 Tools10 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(); }

CSE 6331 © Leonidas Fegaras XML Tools11 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 Tools12 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); } Child:gradstudent Child:name PrinterSAX parser

CSE 6331 © Leonidas Fegaras XML Tools13 Example Input Stream Computer Science Smith John... 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: gradstudentChild: namePrinter

CSE 6331 © Leonidas Fegaras XML Tools14 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:

CSE 6331 © Leonidas Fegaras XML Tools15 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 Tools16 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 Tools17 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<len; i++) { names[i] = xpp.getAttributeName(i); values[i] = xpp.getAttributeValue(i); }; return new StartTag(xpp.getName(),new Attributes(names,values)); } else if (eventType == XmlPullParser.END_TAG) return new EndTag(xpp.getName()); else if (eventType == XmlPullParser.TEXT) { int[] v = new int[2]; char[] ch = xpp.getTextCharacters(v); return new CData(new String(ch,v[0],v[1])); }}

CSE 6331 © Leonidas Fegaras XML Tools18 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 Tools19 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 Tools20 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: <xsl:stylesheet version=’1.0’ xmlns:xsl=’http//

CSE 6331 © Leonidas Fegaras XML Tools21 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 Tools22 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. Example: <xsl:stylesheet version = ’1.0’ xmlns:xsl=’

CSE 6331 © Leonidas Fegaras XML Tools23 Copy the Entire Document <xsl:stylesheet version = ’1.0’ xmlns:xsl=’

CSE 6331 © Leonidas Fegaras XML Tools24 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 Variables can be used to name data: value Variables are used as {$x} in XPaths.

CSE 6331 © Leonidas Fegaras XML Tools25 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); }