Home > Articles > Programming > Java

Introducing Ajax

  • Print
  • + Share This
This chapter is from the book

2.6 An Ajax Encounter of the Third Kind

The fifth part of Ajax, an optional part, isn't for the faint of heart. It transcends the "mad scientist stuff" into the realm of the magical, and it is called eXtensible Stylesheet Language for Transformations, or XSLT. In other words, if Ajax really was mad science and it was taught in school, this would be a 400-level course. Why? The reason is that the technology is both relatively new and very, very browser dependent. However, when it works, this method provides an incredible experience for the user.

2.6.1 XSLT

XSLT is an XML-based language that is used to transform XML into other forms. XSLT applies a style sheet (XSLT) as input for an XML document and produces output—in most cases, XHTML or some other form of XML. This XHTML is then displayed on the browser, literally in the "wink of an eye."

One of the interesting things about XSLT is that, other than the XML being well formed, it really doesn't make any difference where the XML came from. This leads to some interesting possible sources of XML. For example, as you are probably aware, a database query can return XML. But did you know that an Excel spreadsheet can be saved as XML? XSLT can be used to transform any XML-derived language, regardless of the source.

Listing 2-9 shows a simple Internet Explorer–only web page along the same lines as the earlier examples. By using XSLT and the XMLHttpRequest object to retrieve both the XML and XSLT shown in Listing 2-10, it is extremely flexible. This is because after the initial page is loaded, any conceivable page can be generated simply by changing the XML and/or the XSLT. Sounds pretty powerful, doesn't it?

Listing 2-9. A Simple IE-Only Web Page

<html>
  <head>
    <title>AJAX Internet Explorer Flavor</title>
    <script language="javascript">
var dom = new ActiveXObject('MSXML2.FreeThreadedDOMDocument.3.0');
var xslt = new ActiveXObject('MSXML2.FreeThreadedDOMDocument.3.0');
var objXMLHTTP;

/*
    Obtain the initial XML document from the web server.
*/
function initialize()
{
  doPOST(true);
}

/*
    Use the XMLHttpRequest to communicate with a web service.
*/
function doPOST(blnState) {
  var strURL = 'http://localhost/AJAX/msas.asmx';

  objXMLHTTP = new ActiveXObject('Microsoft.XMLHTTP');

  objXMLHTTP.open('POST',strURL,true);

  if(blnState)
    objXMLHTTP.setRequestHeader('SOAPAction','http://
tempuri.org/getState');
  else

  objXMLHTTP.setRequestHeader('SOAPAction','http://tempuri.org/getXML');

  objXMLHTTP.setRequestHeader('Content-Type','text/xml');

  objXMLHTTP.onreadystatechange = stateChangeHandler;

  try
  {
    objXMLHTTP.send(buildSOAP(blnState));
  }
  catch(e)
  {
  alert(e.description);
  }
}

/*
    Construct a SOAP envelope.
*/
function buildSOAP(blnState) {
  var strSOAP = '<?xml version="1.0" encoding="UTF-8"?>';
  strSOAP += '<soap:Envelope
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">';
  strSOAP += '<soap:Body>';

  if(blnState)
  {
    strSOAP += '<getState xmlns="http://tempuri.org/">';
    strSOAP += '<state_abbreviation/>';
    strSOAP += '</getState>';
  }
  else
  {
    strSOAP += '<getXML xmlns="http://tempuri.org/">';
    strSOAP += '<name>xsl/state.xsl</name>';
    strSOAP += '</getXML>';
  }

  strSOAP += '</soap:Body>';
  strSOAP += '</soap:Envelope>';

  return(strSOAP);
}

/*
    Handle server response to XMLHTTP requests.
*/
function stateChangeHandler()
{
  if(objXMLHTTP.readyState == 4)
    try
    {
      var work = new ActiveXObject('MSXML2.FreeThreadedDOMDocument.3.0');

      work.loadXML(objXMLHTTP.responseText);

      switch(true) {
        case(work.selectNodes('//getStateResponse').length != 0):
          dom.loadXML(objXMLHTTP.responseText);
          doPOST(false);

          break;
        case(work.selectNodes('//getXMLResponse').length != 0):
          var objXSLTemplate = new
ActiveXObject('MSXML2.XSLTemplate.3.0');

xslt.loadXML(work.selectSingleNode('//getXMLResult').firstChild.xml);

          objXSLTemplate.stylesheet = xslt;

          var objXSLTProcessor = objXSLTemplate.createProcessor;

          objXSLTProcessor.input = dom;
          objXSLTProcessor.transform();

          document.getElementById('select').innerHTML =
objXSLTProcessor.output;

          break;
        default:
          alert('error');

          break;
      }
    }
    catch(e) { }
}
    </script>
  </head>
  <body onload="initialize()">
  <div id="select"></div>
</html>

Listing 2-10. The XML and XSLT Part

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="html" version="1.0" encoding="UTF-8" indent="yes"/>

  <xsl:template match="/">
    <xsl:element name="select">
      <xsl:attribute name="id">state</xsl:attribute>
      <xsl:attribute name="name">selState</xsl:attribute>
      <xsl:apply-templates select="//Table[country_id = 1]"/>
    </xsl:element>
  </xsl:template>

  <xsl:template match="Table">
    <xsl:element name="option">
      <xsl:attribute name="value"><xsl:value-of
select="state_abbreviation"/></xsl:attribute>
      <xsl:value-of select="state_name"/>
    </xsl:element>
  </xsl:template>
</xsl:stylesheet>

2.6.2 Variations on a Theme

At first glance, the JavaScript in the previous example appears to be very similar to that shown in Listing 2-7; however, nothing could be further from the truth. The first of these differences is due to two calls being made to a web service and the use of XSLT to generate the HTML to be displayed in the browser. Let's look at this in a little more detail.

First, the only thing that the initialize function does is call another function, doPOST, passing a true. Examining doPOST reveals that the purpose of the true is to indicate what the SOAPAction in the request header is, http://tempuri.org/getState to get information pertaining to states and provinces from the web service, or http://tempuri.org/getXML to get XML/XSLT from the web service. The first time through, however, we're getting the XML.

The second difference, also in doPOST, is the addition of a call to buildSOAP right smack in the middle of the XMLHttpRequest object's send. This is how arguments are passed to a web service, in the form of text—a SOAP request, in this instance. Checking out buildSOAP, you'll notice that Boolean from doPOST is passed to indicate what the body of the SOAP request should be. Basically, this is what information is needed from the web service, states or XSLT.

You'll remember the stateChangeHandler from the earlier set of examples, and although it is similar, there are a few differences. The first thing that jumps out is the addition of a "work" XML document that is loaded and then used to test for specific nodes; getStateResponse and getXMLResponse. The first indicates that the SOAP response is from a request made to the web service's getState method, and the second indicates a response from the getXML method. Also notice the doPOST with an argument of false in the part of the function that handles getState responses; its purpose is to get the XSLT for the XSL transformation.

Speaking of a transformation, that is the purpose of the code that you might not recognize in the getXML portion of the stateChangeHandler function. Allow me to point out the selectSingleNode method used, the purpose of which is to remove the SOAP from the XSLT. The reason for this is that the XSLT simply won't work when wrapped in a SOAP response. The final lines of JavaScript perform the transformation and insert the result into the page's HTML.

The use of XSLT to generate the HTML "on the fly" offers some interesting possibilities that the other two methods of implementing Ajax do not. For instance, where in the earlier example the look of the page was dictated by the hard-coded HTML, this doesn't have to be the case when using XSLT. Consider for a moment the possibility of a page using multiple style sheets to change the look and feel of a page. Also, with the speed of XSLT, this change would occur at Windows application speeds instead of the usual crawl that web applications proceed at.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020