XML for E-commerce IV Helena Ahonen-Myka

In this part... n Some solutions for delivering dynamic content n Example of using XML

Solutions for delivering dynamic content n CGI (e.g. Perl, PHP) n Java servlets n Java Server Pages (JSP) n Extensible Server Pages (XSP)

CGI n Server starts external programs using CGI interface (input, output, requests) n a new process is started and the program code is loaded each time a request occurs (even when simultaneous requests) n stateless n any programming languages: Perl, PHP are popular

Perl CGI package #!/usr/bin/perl use CGI qv(:standard); print header(), start_html(”Hello param($name)!”), h1(”Hello param($name)!”), end_html(); n Assume: name is a form field:

PHP #!/usr/local/bin/php > <?php echo ”Hello $name !”; ?>

Java servlets n Java programs that run on a web server and build web pages n each request handled by a thread (light) n only one copy of the code (for simultaneous requests) n maintaining a state easier

public class helloWWW extends HttpServlet { public void doGet (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType(”text/html”); printWriter out = response.getWriter(); out.println(” \n” + ” \n” + ” Hello” + request.getParameter(”name”) + ”! ” + ” \n” + ” Hello” + request.getParameter(”name”) + ”! \n” + ” ”); }}

Java Server Pages (JSP) n static HTML + dynamic parts n within the code, e.g. n JSP pages are converted to Java servlets (the first time the page is requested) and the servlet is compiled

Hello <% request.getParameter(”name”) %> Hello <% request.getParameter(”name”) %>

Extensible Server Pages (XSP) n XML pages with embedded logic n processing can be done before the styling and presentation is done n therefore the result can easily be used in further processing (cf. JSP is used to generate output) n and the logic is separated from presentation

<?xml-stylesheet href=”myStylesheet.xsl” type=”text/xsl”?> <xsp:page language=”java” xmlns:xsp= ” private static int numHits = 0; private synchronized int getNumHits() { return ++numHits;} Hit Counter I’ve been requested getNumHits() times.

Example n The Foobar Public Library n mytechbooks.com n customers of mytechbooks.com

The Foobar Public Library n suppliers can add new books that they are sending to the library n an HTML page with a form: <form method=”POST” action=” … Title: Publisher: …

addBooks.pl n a Perl CGI script: reads the data received from the user and produces XML data n each new entry is appended to an existing file

Writing an XML file $bookFile = ”/home/foobar/books/books.txt”; use CGI; $query = new CGI; $title = $query->param(’title’); $publisher = $query->(’publ’); … if (open(FILE, ”>>”. $bookFile)) { print FILE ” \n”; print FILE ” \n; … print FILE ” \n\n”;

Notes: n Only an XML fragment is generated: no declaration, no root element

n Some other portion of the library’s application periodically reads the XML data and updates the library’s catalog: this part also removes the entries from the list of new entries n providing a listing of new available books: add an XML declaration etc.

supplyBooks.pl $bookFile = ”/home/foobar/books/books.txt” open(FILE, $bookFILE) || die ”Could’t open $bookFile.”; print ”Content-type: text/plain\n\n”; print ” \n”; while ( ) { print ”$_”; } print ” \n”; close(FILE);

mytechbooks.com n can make HTTP requests (supplyBooks.pl) and receives a list of books in XML n needs a listing of new technical books on their own Web page n wants to advertise (push technology)

Filtering the XML data n only computer-related books are to be included (Foobar Library has several other subjects as well) n subject information is an attribute of the book element n filter out all the books whose subject is not ”Computers”

computerBooks.xsl … <xsl:apply-templates />

XSL stylesheet: book Author: Publisher: Pages: Price: /servlets/BuyBookServlet?isbn=

XSLT from a servlet import... public class ListBooksServlet extends HttpServlet { private static final String hostname=”foobar.com”; private static final int portNumber = 80; private static final String file =”/cgi/supplyBooks.pl”; private static final String stylesheet = ”/home/…/computerBooks.xsl”; public void service(HttpServletRequest req, HttpServletResponse res) throws … { res.setContentType(”text/html”); URL getBooksURL = new URL(”http”,hostname,portNumber,file); InputStream in = getBooksURL.openStream(); // transform XML into HTML }}

Notes: n Servlet requests the Foobar Public Library’s application (supplyBooks.pl) through an HTTP request, and gets the XML response in an InputStream n this stream is used as a parameter to the XSLT processor, as well as the XSL stylesheet defined as a constant in the servlet

Invoking transformations n There is current no general API that specifies how XSLT transformations can occur programmatically: each processor vendor should have classes that allow a transformation to be invoked from Java code

Invoking transformations n Apache Xalan: XSLTProcessor class in the org.apache.xalan.xslt package n parameters: the XML file to process, the stylesheet to apply, and output stream (servlet output stream can be used)

… URL getBooksURL = new URL (”http”, hostname, portNumber, file); InputStream in = getBooksURL.openStream(); try { XSLTProcessor processor = XSLTProcessorFactory.getProcessor(); processor.process(new XSLTInputSource(in), new XSLTInputSource ( new FileInputStream(stylesheet)), new XSLTResultTarget( res.getOutputStream())); } catch (Exception e) {…} }

Push vs. pull n Pull: the user writes an URL or follows a link, or an application makes an HTTP request n Push: data is delivered to the user without the user’s active request; e.g. which new items are available, special offers...

Personalized start pages and RSS n Personalized start pages: e.g. Netscape’s My Netscape and Yahoo’s My Yahoo n Rich Site Summary (RSS): an XML application, which defines channels n a channel provides quick info about e.g. a company’s products (for display in a portal-style framework)

RSS channel n title of the channel n description of the channel n image or logo n items, each item may contain title, description and hyperlink

… in our example n mytechbooks.com would like to create an RSS channel that provides new book listings: interested clients can jump directly to buying an item n a channel is registered with Netscape Netcenter n Netcenter will automatically update RSS channel content

<!DOCTYPE rss PUBLIC ”-//Netscape Communications//DTD RSS 0.91//EN” ” mytechbooks.com New Listings Your online source for technical material, computers, and computing books! en-us …

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Transformation into RSS n an XSLT transformation can transform the book elements to item elements: n book -> item n title -> title n saleDetails/isbn -> link (isbn as param.) n description -> description

Validating the RSS channel n validate.tmpl n there are some constraints that cannot be enforced by the DTD n RSS channel can be a servlet, CGI script, a static file...

Registering the channel n The channel is published to Netcenter (or other service provider) n n once the valid channel is accepted, instructions how to add the channel to a web page is sent by

Use n button or link is added to the mytechbooks.com web page: ”Add this site to My Netscape” n inclusion in the Netscape Open Directory

Not restricted to Netscape n The same RSS format can (and is) used in different applications n format is simple and generic: suitable for many purposes