XML for E-commerce IV

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XML for E-commerce IV

• Helena Ahonen-Myka

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In this part...

• Some solutions for delivering dynamic content
• Example of using XML

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Solutions for delivering dynamic content

• CGI (e.g. Perl, PHP)
• Java servlets
• Java Server Pages (JSP)
• Extensible Server Pages (XSP)

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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

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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()
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PHP
!/usr/local/bin/php lthtml title lt? echo Hello
name ! ?gt gt ltbodygt lt?php
echo Hello name ! ?gt
lt/bodygt lt/htmlgt
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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

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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(lt!DOCTYPE HTML PUBLIC gt \n
lthtmlgt \n
ltheadgtlttitlegtHello
request.getParameter(name) !lt/titlegt
lt/headgt\n ltbodygt\n
lth1gtHello
request.getParameter(name) !lt/ lt/h1gt\n
lt/bodygtlt/htmlgt)
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Java Server Pages (JSP)

• static HTML dynamic parts
• within the code, e.g. lt ...scripting gt
• JSP pages are converted to Java servlets (the
  first time the page is requested) and the servlet
  is compiled

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lt!DOCTYPE HTML PUBLIC gt lthtmlgt
ltheadgtlttitlegtHello lt
request.getParameter(name) gtlt/titlegt
lt/headgt ltbodygt lth1gtHello lt
request.getParameter(name) gtlt/h1gt
lt/bodygt lt/htmlgt
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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

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lt?xml version1.0 ?gt lt?xml-stylesheet
hrefmyStylesheet.xsl
typetext/xsl?gt ltxsppage languagejava
xmlnsxsp
http//www.apache.org/1999/XSP/Coregt ltxsplogic
gt private static int numHits 0 private
synchronized int getNumHits() return
numHits lt/xsplogicgt ltpagegtlttitlegtHit
Counterlt/titlegt ltpgtIve been requested
ltxspexprgtgetNumHits() lt/xspexprgt
times.lt/pgtlt/pagegtlt/xsppagegt
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Example

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

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The Foobar Public Library

• suppliers can add new books that they are sending
  to the library
• an HTML page with a form

ltform methodPOST
actionhttp//www.foo.com/cgi/addBook.plgt
Titleltinput typetext nametitle
size20gt Publisherltinput typetext
namepubl size20gt lt/formgt
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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

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Writing an XML file
bookFile /home/foobar/books/books.txt use
CGI query new CGI title
query-gtparam(title) publisher
query-gt(publ) if (open(FILE, gtgt .
bookFile)) print FILE ltbook subject\
. subject . \gt\n print FILE
lttitlegtlt!CDATA . title . gtlt/titlegt\n
print FILE lt/bookgt\n\n
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Notes

• Only an XML fragment is generated no
  declaration, no root element

ltbook subjectFictiongt lttitlegtlt!CDATASecond
Foundationgtlt/titlegt ltauthorgtlt!CDATAIsaac
Asimovgtlt/authorgt ltpublishergtlt!CDATABantam
Booksgtlt/publishergt ltnumPagesgt279lt/numPagesgt
ltsaleDetailsgtltisbngt0553293362lt/isbngt
ltpricegt5.59lt/price gtlt/saleDetailsgt
ltdescriptiongtlt!CDATAAfter the First
Foundationgt lt/descriptiongt lt/bookgt
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• Some other portion of the librarys application
  periodically reads the XML data and updates the
  librarys 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.

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supplyBooks.pl
bookFile /home/foobar/books/books.txt open(F
ILE, bookFILE) die Couldt open
bookFile. print Content-type
text/plain\n\n print lt?xml version\1.0\?gt\n
print ltbooksgt\n while (ltFILEgt) print
_ print lt/booksgt\n close(FILE)
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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)

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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

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computerBooks.xsl
ltxslstylesheet xmlnshttp//.
version1.0gt ltxsltemplate matchbooksgt
lthtmlgtltheadgtlt/headgt ltbodygt lt!--
user interface details --gt
ltxslapply-templates
selectbook_at_subjectComputers /gt
lt!-- user interface details --gt
lt/bodygt lt/xsltemplategt lt/xslstylesheetgt
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XSL stylesheet book
ltxsltemplate matchbookgt lttablegt
lttrgtlttdgtltxslvalue-of selecttitle
/gtlt/tdgtlt/trgt lttrgtlttdgt Author
ltxslvalue-of selectauthor /gtltbr /gt
Publisher ltxslvalue-of selectpublisher /gtltbr
/gt Pages ltxslvalue-of selectnumPages
/gtltbr /gt Price ltxslvalue-of
selectsaleDetails/price /gtltbr /gt ltbr
/gt ltxslelement nameagt
ltxslattribute namehrefgt
/servlets/BuyBookServlet?isbn
ltxslvalue-of selectsaleDetails/isbn /gt
lt/xslattributegtlt/xslelementgtlt/tdgtlt/trgtlt/tab
legt lt/xsltemplategt
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XSLT from a servlet
import ... public class ListBooksServlet extends
HttpServlet private static final String
hostnamefoobar.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/htm
l) URL getBooksURL new
URL(http,hostname,portNumber,file)
InputStream in getBooksURL.openStream()
// transform XML into HTML
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Notes

• Servlet requests the Foobar Public Librarys
  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

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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

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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)

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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)
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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
  users active request e.g. which new items are
  available, special offers...

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Personalized start pages and RSS

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

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RSS channel

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

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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

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lt?xml version1.0gt lt!DOCTYPE rss PUBLIC
-//Netscape Communications//DTD RSS 0.91//EN
http//my.netscape.com/publish/formats/rss-0.9
1.dtdgt ltrss version0.91gt ltchannelgt
lttitlegtmytechbooks.com New Listingslt/titlegt
ltlinkgthttp//www.newInstance.com/javaxml/techbooks
lt/linkgt ltdescriptiongtYour online
source for technical material, computers, and
computing books!lt/descriptiongt
ltlanguagegten-uslt/languagegt
ltimagegtlt/imagegt ltitemgtlt/itemgt
ltitemgtlt/itemgt lt/channelgt lt/rssgt
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ltitemgt lttitlegtJava Servlet
Programminglt/titlegt ltlinkgt
http//mytechbooks.com/buy.xsp?isbn156592391X
lt/linkgt ltdescriptiongt
This book is a superb introduction to Java
servlets and their various
communications mechanisms.
lt/descriptiongt lt/itemgt
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Transformation into RSS

• an XSLT transformation can transform the book
  elements to item elements
• book -gt item
• title -gt title
• saleDetails/isbn -gt link (isbn as param.)
• description -gt description

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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...

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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

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Use

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

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Not restricted to Netscape

• The same RSS format can (and is) used in
  different applications
• format is simple and generic suitable for many
  purposes