XML for E-commerce IV

XML for E-commerce IV Helena Ahonen-Myka

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

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

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

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

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

Java servlets • Java programs that run on a web server and build web pages • each request handled by a thread (light) • only one copy of the code (for simultaneous requests) • 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(”<!DOCTYPE HTML PUBLIC …> \n” + ”<html> \n” + ”<head><title>Hello” + request.getParameter(”name”) + ”!</title>” + ”</head>\n” + ”<body>\n” + ”<h1>Hello” + request.getParameter(”name”) + ”!</ </h1>\n” + ”</body></html>”); }}

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

<!DOCTYPE HTML PUBLIC …> <html> <head><title>Hello <% request.getParameter(”name”) %></title> </head> <body> <h1>Hello <% request.getParameter(”name”) %></h1> </body> </html>

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

<?xml version=”1.0” ?> <?xml-stylesheet href=”myStylesheet.xsl” type=”text/xsl”?> <xsp:page language=”java” xmlns:xsp= ”http://www.apache.org/1999/XSP/Core”> <xsp:logic> private static int numHits = 0; private synchronized int getNumHits() { return ++numHits;} </xsp:logic> <page><title>Hit Counter</title> <p>I’ve been requested <xsp:expr>getNumHits() </xsp:expr> times.</p></page></xsp:page>

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

The Foobar Public Library • suppliers can add new books that they are sending to the library • an HTML page with a form: <form method=”POST” action=”http://www.foo.com/cgi/addBook.pl”> … Title:<input type=”text” name=”title” size=”20”> Publisher:<input type=”text” name=”publ” size=”20”> … </form>

addBooks.pl • a Perl CGI script: reads the data received from the user and produces XML data • 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 ”<book subject=\”” . $subject . ”\”>\n”; print FILE ” <title><![CDATA[” . $title . ”]]></title>\n; … print FILE ”</book>\n\n”;

Notes: • Only an XML fragment is generated: no declaration, no root element <book subject=”Fiction”> <title><![CDATA[Second Foundation]]></title> <author><![CDATA[Isaac Asimov]]></author> <publisher><![CDATA[Bantam Books]]></publisher> <numPages>279</numPages> <saleDetails><isbn>0553293362</isbn> <price>5.59</price ></saleDetails> <description><![CDATA[After the First Foundation…]]> </description> </book>

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 • 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 $bookFile.”; print ”Content-type: text/plain\n\n”; print ”<?xml version=\”1.0\”?>\n”; print ”<books>\n”; while (<FILE>) { print ”$_”; } print ”</books>\n”; close(FILE);

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

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

computerBooks.xsl <xsl:stylesheet xmlns:”http://….” version=”1.0”> <xsl:template match=”books”> <html><head>…</head> <body>  <xsl:apply-templates select=”book[@subject=’Computers’]” />  </body> </xsl:template> </xsl:stylesheet>

XSL stylesheet: book <xsl:template match=”book”> <table> <tr><td><xsl:value-of select=”title” /></td></tr> <tr><td> Author: <xsl:value-of select=”author” /><br /> Publisher: <xsl:value-of select=”publisher” /><br /> Pages: <xsl:value-of select=”numPages” /><br /> Price: <xsl:value-of select=”saleDetails/price” /><br /> <br /> <xsl:element name=”a”> <xsl:attribute name=”href”> /servlets/BuyBookServlet?isbn= <xsl:value-of select=”saleDetails/isbn” /> </xsl:attribute></xsl:element></td></tr></table> </xsl:template>

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: • Servlet requests the Foobar Public Library’s application (supplyBooks.pl) through an HTTP request, and gets the XML response in an InputStream • 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 • 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 • Apache Xalan: XSLTProcessor class in the org.apache.xalan.xslt package • 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 • Pull: the user writes an URL or follows a link, or an application makes an HTTP request • 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 • Personalized start pages: e.g. Netscape’s My Netscape and Yahoo’s My Yahoo • Rich Site Summary (RSS): an XML application, which defines channels • a channel provides quick info about e.g. a company’s products (for display in a portal-style framework)

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

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

<?xml version=”1.0”> <!DOCTYPE rss PUBLIC ”-//Netscape Communications//DTD RSS 0.91//EN” ”http://my.netscape.com/publish/formats/rss-0.91.dtd”> <rss version=”0.91”> <channel> <title>mytechbooks.com New Listings</title> <link>http://www.newInstance.com/javaxml/techbooks </link> <description>Your online source for technical material, computers, and computing books!</description> <language>en-us</language> <image>…</image> <item>…</item> <item>…</item> </channel> </rss>

<item> <title>Java Servlet Programming</title> <link> http://mytechbooks.com/buy.xsp?isbn=156592391X </link> <description> This book is a superb introduction to Java servlets and their various communications mechanisms. </description> </item>

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

Validating the RSS channel • http://my.netscape.com/publish/help/ validate.tmpl • there are some constraints that cannot be enforced by the DTD • RSS channel can be a servlet, CGI script, a static file...

Registering the channel • The channel is published to Netcenter (or other service provider) • http://my.netscape.com/publish • once the valid channel is accepted, instructions how to add the channel to a web page is sent by email

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

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

XML for E-commerce IV