xml for e-commerce iv helena ahonen-myka. in this part... n some solutions for delivering dynamic...

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

#!/usr/bin/perl

use CGI qv(:standard);

print header(), start_html(”Hello param($name)!”), h1(”Hello param($name)!”), end_html();

Assume: name is a form field:

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 servletimport ...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

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