Home > Articles > Web Services > XML

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

This chapter is from the book

The XmlTextReader Class

The XmlTextReader class is designed for fast, resource nonintensive access to the contents of an XML file. Unlike the XmlDocument class, the XMLTextReader class does not create a node tree of the entire document in memory. Rather, it processes the XML as a forward-only stream. The entire XML document is never available at the same time (as is the case with the XmlDocument class)—your code can extract individual items from the XML file as they stream by.

In some ways the XmlTextReader class is similar to the SAX model covered in Chapter 11, and in fact, the .NET programmer would tend to use the XmlTextReader class for the same types of processing that SAX would be used for. There is a major difference between the two models, however. SAX uses a push model in which the XML processor uses events to inform the host program that node data is available, and the program can use the data or not as its needs dictate. The data is pushed from the XML processor to the host, and it can be accepted or ignored. As an analogy, think of a Chinese dim sum restaurant where the available food is brought around on carts and you select what you want.

In contrast, the XmlTextReader class uses a pull model. The host program requests that the XML processor read a node, and then requests data from that node as needed. The host program pulls the data from the processor as it is needed. Pull processing is analogous to a traditional restaurant where you request items from a menu. A pull model has numerous advantages over a push model for XML processing. Perhaps most important is that a push model can easily be built on top of a pull model, while the reverse is not true.

The XmlTextReader class operates by stepping through the nodes of an XML document, one at a time, under the control of the host program. At any given time, there is a current node. For the current node, the host program can determine the type of the node, its attributes (if any), its data, and so on. Once the needed information about the current node has been obtained, the program will step to the next node. In this manner the entire XML file can be processed.

The XmlTextReader class has a large number of public properties and methods. The ones you will need most often are explained in Table 13.1 and Table 13.2.

Table 13.1 Commonly Needed Properties of the XmlTextReader Class

Property

Description

AttributeCount

Returns the number of attributes of the current node

Depth

Returns the depth (nesting level) of the current node

EOF

Returns True if the XML reader is at the end of the file

HasAttributes

Returns True if the current node has attributes

HasValue

Returns True if the current node can have a value

IsEmptyElement

Returns True if the current node is an empty element (for example, <ElementName/>)

Item

Returns the value of an attribute

LocalName

Returns the name of the current node without any namespace prefix

Name

Returns the name of the current node with any namespace prefix

NodeType

Returns the type of the current node as an XmlNodeType (see Table 13.3)

Value

Returns the value of the current node


Table 13.2 Commonly Needed Methods of the XmlTextReader Class

Method

Description

Close()

Closes the XML file and reinitializes the reader.

GetAttribute(att)

Gets the value of an attribute. Att is a number specifying the position of the attribute, with the first attribute being 0, or a string specifying the name of the attribute.

IsStartElement()

Returns True if the current node is a start element or an empty element.

MoveToAttribute(att)

Moves to a specific attribute. Att is a number specifying the position of the attribute, with the first attribute being 0, or a string specifying the name of the attribute.

MoveToElement()

Moves to the element that contains the current attribute.

MoveToFirstAttribute()

Moves to the first attribute.

MoveToNextAttribute()

Moves to the next attribute.

Read()

Reads the next node from the XML file. Returns True on success or False if there are no more nodes to read.


Table 13.3 XmlNodeType Values Returned by the NodeType Property

Value

Meaning

Attribute

An attribute

CDATA

A CDATA section

Comment

A comment

Document

The document node (root element)

DocumentType

A DOCTYPE element

Element

An element (opening tag)

EndElement

The end of an element (closing tag)

EntityReference

An entity reference

ProcessingInstruction

An XML processing instruction

Text

The text content of an element

XmlDeclaration

The XML declaration element


The basic steps required to use the XmlTextReader class are as follows:

  1. Create an instance of the class, passing the name of the XML file to process as an argument to the class constructor.

  2. Create a loop that executes the Read() method repeatedly until it returns False, which means that the end of the file has been reached.

  3. In the loop, determine the type of the current node.

  4. Based on the node type, either ignore the node or retrieve node data as needed.

Listing 13.1 presents an example of using the XmlTextReader class. It is an ASP Web page, with the script components written using the C# language. The script opens an XML file and processes it using the XmlTextReader class. The root element in the file, its child element, and their attributes and data are formatted as HTML and written to the output for display in the browser.

The script defines a class called DisplayXmlFile that does all of the work. This class contains one public method, ReadDoc(), that is passed the name of the XML file to be processed and returns the HTML to be displayed in the document. It also contains two private methods: ProcessXml(), which performs the actual processing of the XML file, and Spaces(), which is a utility function to provide indentation to format the output.

The script also contains a procedure named Page_Load(). This is an event procedure that is called automatically when the browser first loads the page. Code in this procedure creates an instance of the DisplayXml class, and then calls its ReadDoc() method, passing the name of the XML file to be processed. The HTML returned by this method is displayed by assigning it to the InnerHTML property of a <div> element in the page.

Figure 13.1 shows the output when this script is used to process Listing1506.xml, an XML file that is presented in Chapter 15. Though not visible in the figure, the data (attribute and element values) are displayed in blue while the remainder of the document is in black.

Figure 13.1 An XML file displayed in Internet Explorer by the script in Listing 13.1

Listing 13.1 Using the XmlTextReader Class to Read Data from an XML File

<%@ Import Namespace="System.Xml" %>
<script language="C#" runat=server>
 public class DisplayXmlFile
 // This is the class that reads and processes the XML file.
 {
  StringBuilder result = new StringBuilder();
  public string ReadDoc(String XmlFileName) {
   XmlTextReader xmlReader = null;
	try {
	  // Create an instance of the XMLTextReader.
	  xmlReader = new XmlTextReader(XmlFileName);
	  // Process the XML file.
	  ProcessXml(xmlReader);
	  }
	catch (Exception e){
	  result.Append("The following error occurred: " + 
      e.ToString());
	  }    
    finally 
	  {
	  if (xmlReader != null)
	  xmlReader.Close();
	  }
    return result.ToString();
  }
 private void ProcessXml(XmlTextReader xmlReader) {
  // This method reads the XML file and generates the output HTML.
  while (xmlReader.Read()) {
  // Process a start of element node.
  if (xmlReader.NodeType == XmlNodeType.Element) {
   result.Append(spaces(xmlReader.Depth*3));
   result.Append("&lt;" + xmlReader.Name);
   if (xmlReader.AttributeCount > 0) {
    while (xmlReader.MoveToNextAttribute()) {
     result.Append("&nbsp" + xmlReader.LocalName + 
      "=<font color=#0000ff>" + xmlReader.Value +
      "</font>&nbsp");
    }
   }
    result.Append("&gt;<br>");
  // Process an end of element node.
  } else if (xmlReader.NodeType == XmlNodeType.EndElement) {
    result.Append(spaces(xmlReader.Depth*3));
    result.Append("&lt;/" + xmlReader.Name + "&gt;<br>");
  // Process a text node.
  } else if (xmlReader.NodeType == XmlNodeType.Text) {
    if (xmlReader.Value.Length != 0) {
     result.Append(spaces(xmlReader.Depth*3));
     result.Append("<font color=#0000ff>" + xmlReader.Value + 
       "<br></font>");
  }
  }
 }
 }

private string spaces(int n) {
// Returns the specified number of non-breaking
// spaces (&nbsp;).
  string s = "";
  for (int i=0; i < n; i++) { 
	 s += "&nbsp;";
	}
  return s;
 }
} //End DisplayXmlFile Class
private void Page_Load(Object sender, EventArgs e){
  // Create a class instance.
  DisplayXmlFile DisplayXmlFileDemo = new DisplayXmlFile();
  // Add the HTML generated by the class to the HTML document.
  show.InnerHtml = DisplayXmlFileDemo.ReadDoc(Server.MapPath("list1506.xml"));
}
</script>
<html>
<head>
</head>
<body>
 <font size="4">Using the XmlTextReader Class</font><p>
 <div id="show" runat="server"/>
</body>
</html>
  • + 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