1. Java WWW Week 10 Version 2.1 Mar 2008 Slide 1j.c.westlake@staffs.ac.uk Java (JSP) and XML  Format of lecture: What is XML? A sample XML file… How to use XML with JSP  Example code for parsing an XML file in JSP

2. Java WWW Week 10 Version 2.1 Mar 2008 Slide 2j.c.westlake@staffs.ac.uk What is XML?  XML is principally concerned with the description and structure of data (content & presentation are separate)  Traditional methods of data storage and exchange employ a variety of schemes Electronically, these usually are of the form of simple text files (Comma Separated Values etc.) or binary files  Both methods have their own advantages and disadvantages CSV files contain data that can be easily read but lack a description of their own format Binary files contain data and a description of its data format (as a Word document does) but are proprietary schemes that require specific applications to read them

3. Java WWW Week 10 Version 2.1 Mar 2008 Slide 3j.c.westlake@staffs.ac.uk What is XML?  XML stands for eXtensible Markup Language  Developed by World Wide Web Consortium (W3C)  Aims to provide the best of both worlds Stores data in an easy to read text format Also contains a description of the data  Open standard - looks similar to HTML (large user base) except the extensible nature of XML allows for the creation of user-defined tags  It is not a replacement for HTML (although it may eventually supplant it)

4. Java WWW Week 10 Version 2.1 Mar 2008 Slide 4j.c.westlake@staffs.ac.uk What is XML?  XML offers a standard method for storing structured data  Language independence (English, Chinese etc.)  Hierarchical structure allows for simple and efficient querying/parsing of the document  Simple data interchange between applications and/or distributed objects

5. Java WWW Week 10 Version 2.1 Mar 2008 Slide 5j.c.westlake@staffs.ac.uk What is XML?  Can improve upon and replace existing EDI (Electronic Document Interchange) solutions such as EDIFACT  Websites gain by having content and presentation separate A site could be developed purely in XML  Cost benefits No need for private EDI networks – the Internet used as exchange medium Reduced time to implement/reduced maintenance

6. Java WWW Week 10 Version 2.1 Mar 2008 Slide 6j.c.westlake@staffs.ac.uk Illustrative Example Paper-based or Simple Text File Jonathan Westlake Staffordshire University j.c.westlake@staffs.ac.uk Comma Separated Values Jonathan,Westlake,Staffordshire University,j.c.westlake@staffs.ac.uk Binary – a string of 0s and 1s 0101 1001 0111 0110 0110 0001 0110 1110 0010 0000 etc.

7. Java WWW Week 10 Version 2.1 Mar 2008 Slide 7j.c.westlake@staffs.ac.uk Illustrative Example Simple ‘Freeform’ (i.e. without an XML schema) XML File Jonathan Westlake Staffordshire University j.c.westlake@staffs.ac.uk

8. Java WWW Week 10 Version 2.1 Mar 2008 Slide 8j.c.westlake@staffs.ac.uk How to use XML with JSP  XML is a big topic!  We are just going to look at one of the more fundamental aspects of XML  An XML parser simply checks that your XML document is syntactically correct (well-formed) and contains correctly formatted data (valid)  Once an XML document is parsed, the information it contains is accessible inside our web application  There are two ways of parsing an XML document – Simple API for XML (SAX) and Document Object Model (DOM) reference link

9. Java WWW Week 10 Version 2.1 Mar 2008 Slide 9j.c.westlake@staffs.ac.uk SAX Parser  Event Driven : An event is triggered each time the parser encounters a beginning, or ending tag

10. Java WWW Week 10 Version 2.1 Mar 2008 Slide 10j.c.westlake@staffs.ac.uk DOM Parser  A tree representing the document is built in memory.

11. Java WWW Week 10 Version 2.1 Mar 2008 Slide 11j.c.westlake@staffs.ac.uk DOM Tree Structure contacts---contact | |---name | | | |---firstname | | └ ---Text | | | └ ---lastname | └ ---Text | |---workplace | └ ---Text | └ ---email └ ---Text For our contacts example

12. Java WWW Week 10 Version 2.1 Mar 2008 Slide 12j.c.westlake@staffs.ac.uk Standard DOM Parsing  Searching for a contact based on their email address  Create a Document object  Load the XML file into the Document  Using iterations over the Document nodes, you can access any of the values or attributes that are stored in the XML file  When you find the record that contains the email address that you are looking for, do something with the information

13. Standard DOM Parsing // Get a factory object (many ways to build a Document, this lets us choose) DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance(); // ensures the factory object returned is set to validate the XML data with the schema docBuilderFactory.setAttribute( "http://java.sun.com/xml/jaxp/properties/schemaLanguage", "http://www.w3.org/2001/XMLSchema"); docBuilderFactory.setValidating(true); docBuilderFactory.setNamespaceAware(true); // get the Document builder object that we will use to build the DOM tree in memory DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder(); // load the XML file into a new Document object Document doc = docBuilder.parse(new File(“myfile.xml”)); // does a bit of extra DOM processing (strips out empty nodes etc.) doc.normalize();

14. Standard DOM Parsing // get the whole node structure NodeList nodelist = getNodeList("/contacts", doc); for(int index = 0; index < nodelist.getLength(); index++) {Node node = nodelist.item(index); if(node.getNodeType(TEXT_NODE)) {if(node.getNodeName().equals(“firstname”)) firstname = node.getNodeValue(); if(node.getNodeName().equals(“lastname”)) lastname = node.getNodeValue(); if(node.getNodeName().equals(“workplace”)) workplace = node.getNodeValue(); if(node.getNodeName().equals(“email”)) email = node.getNodeValue(); if(email.equals(“j.c.westlake@staffs.ac.uk”)) { displayRecord(firstname, lastname, workplace, email); break; }

15. Java WWW Week 10 Version 2.1 Mar 2008 Slide 15j.c.westlake@staffs.ac.uk Standard DOM Parsing Problems  The previous procedure is ok if you have a fairly ‘flat’ XML structure that does not contain many different node types  If you have many contacts stored then it may be very slow to iterate through the nodes until you find the contact you are looking for  For more complex XML documents, you can’t use a simple FOR loop to iterate  You end up with code that looks more like…

16. Java WWW Week 10 Version 2.1 Mar 2008 Slide 16j.c.westlake@staffs.ac.uk Not Nice! Element root = doc.getDocumentElement(); Node configNode = root.getFirstChild(); NodeList childNodes = configNode.getChildNodes(); for (int childNum = 0; childNum < childNodes.getLength(); childNum++) { if ( childNodes.item(childNum).getNodeType() == Node.ELEMENT_NODE ) {Element child = (Element) childNodes.item( childNum ); if ( child.getTagName().equals( "header" ) ) {// Do something with the header System.out.print("Got a header!\n"); }

17. Java WWW Week 10 Version 2.1 Mar 2008 Slide 17j.c.westlake@staffs.ac.uk XPath  XPath (XML Path Language) is a terse (short, non- XML) syntax for addressing portions of an XML document  A typical XPath expression is a Location Path consisting of a string of element or attribute qualifiers separated by forward slashes ("/"), similar in appearance to a file system path  E.g. this gets the email field of the first contact //contact[1]/email  NB would you expect to have seen //contact[0]/...?

18. Java WWW Week 10 Version 2.1 Mar 2008 Slide 18j.c.westlake@staffs.ac.uk Using XPath  We can use the XPath syntax to retrieve any information we like from the Document  XPath is a new(ish) specification and initially it was only available via Java extensions  As of version 1.5 of the JDK, Java now natively supports XPath

19. Search Using XPath // create the XPath and initialize it XPath xPath = XPathFactory.newInstance().newXPath(); // now execute the XPath select statement to get the contact that matches the email address NodeList nodes = (NodeList)xPath.evaluate(//contact[email=‘j.c.westlake@staffs.ac.uk’], nodelist, XPathConstants.NODESET); Node fNameNode = (NodeList) xPath.evaluate(//firstname’], nodes, XPathConstants.NODESET); String firstname = firstNameNode.getNodeValue(); Node lNameNode = (NodeList) xPath.evaluate(//lastname’], nodes, XPathConstants.NODESET); String lastname = lastNameNode.getNodeValue(); Node workNode = (NodeList) xPath.evaluate(//workplace’], nodes, XPathConstants.NODESET); String workplace = workPlaceNode.getNodeValue(); Node emailNode = (NodeList) xPath.evaluate(//email’], nodes, XPathConstants.NODESET); String email = emailNode.getNodeValue();

20. Java WWW Week 10 Version 2.1 Mar 2008 Slide 20j.c.westlake@staffs.ac.uk XMLHelper.java package xmlhelper; import javax.xml.xpath.XPath; import javax.xml.xpath.XPathConstants; import javax.xml.xpath.XPathExpressionException; import javax.xml.xpath.XPathFactory; import org.w3c.dom.Document; import org.w3c.dom.Node; import org.w3c.dom.NodeList; So JSP has access to a set of packages which include DOM and XPath

21. Java WWW Week 10 Version 2.1 Mar 2008 Slide 21j.c.westlake@staffs.ac.uk

22. Java WWW Week 10 Version 2.1 Mar 2008 Slide 22j.c.westlake@staffs.ac.uk getNodeListXPath() public static NodeList getNodeListXPath(String expression, Document target) throws XPathExpressionException { // create the XPath and initialize it XPath xPath = XPathFactory.newInstance().newXPath(); // now execute the XPath select statement NodeList nodeList = (NodeList) xPath.evaluate(expression, target, XPathConstants.NODESET); // return the resulting node return nodeList; }

23. Java WWW Week 10 Version 2.1 Mar 2008 Slide 23j.c.westlake@staffs.ac.uk getBooleanXPath() public static boolean getBooleanXPath(String expression, Document target) throws XPathExpressionException { // create the XPath and initialize it XPath xPath = XPathFactory.newInstance().newXPath(); // now execute the XPath select statement Boolean nodeBoolean = (Boolean)xPath.evaluate(expression, target, XPathConstants.BOOLEAN); // return the resulting node return nodeBoolean.booleanValue(); }

24. Java WWW Week 10 Version 2.1 Mar 2008 Slide 24j.c.westlake@staffs.ac.uk getNumberXPath() public static double getNumberXPath(String expression, Document target) throws XPathExpressionException { // create the XPath and initialize it XPath xPath = XPathFactory.newInstance().newXPath(); // now execute the XPath select statement Double nodeNumber = (Double)xPath.evaluate(expression, target, XPathConstants.NUMBER); // return the resulting node return nodeNumber.doubleValue(); }

25. Java WWW Week 10 Version 2.1 Mar 2008 Slide 25j.c.westlake@staffs.ac.uk getStringXPath() public static String getStringXPath(String expression, Document target) throws XPathExpressionException { // create the XPath and initialize it XPath xPath = XPathFactory.newInstance().newXPath(); // now execute the XPath select statement String nodeText = (String)xPath.evaluate(expression, target, XPathConstants.STRING); // return the resulting node return nodeText; }

26. Java WWW Week 10 Version 2.1 Mar 2008 Slide 26j.c.westlake@staffs.ac.uk Summary  XML is important as it offers: Neutral data exchange Can be built into a web application Can be searched for content using XPath  Java (and therefore JSP) can use XML and Xpath  Used widely in enterprise-scale information systems  No lecture next week but the first revision session in preparation of the module class test (short exam)