Publishers of technology books, eBooks, and videos for creative people

Home > Articles > Web Design & Development > PHP/MySQL/Scripting

XmlReader and XmlWriter

  • Print
  • + Share This
XmlReader and XmlWriter provide an XML interface that is more efficient and easy to use than the DOM access methods of the past. Dale Michalk shows you how to use these tools in your own XML code.

The previous article in this series discussed the DOM API for XML data access in the .NET framework. It models an XML document as a tree of nodes kept in memory while a client is using the document. The top part of Figure 1 shows how the DOM parser produces a tree of nodes. The client access methods allow forward and backward movement, much like the client-side, static cursor in ADO data access on the Microsoft platform. The cost of this type of capability is the resource requirements needed to keep each node in memory. This can present a real problem when document sizes become too large to fit in memory in an efficient manner.

Figure 1 - DOM vs. SAX vs. XmlReader

The SAX API was one of the first attempts in the XML community to solve the problem of parsing large XML documents. The SAX parser uses a streaming model that moves through a document piece by piece and doesn't retain a copy of the nodes once they are traversed. A client implements a set of interfaces that are called by the parser when it passes over nodes in the document. Methods are called for the document, elements, attributes, and other types of nodes. This type of API is called a "push model" because the document information is pushed from the parser to the client. The middle part of Figure 1 illustrates the SAX approach to parsing.

The downside of this approach is that keeping track of the current context of an element or attribute in a complex document can be difficult. The client code must provide some sort of state model to guide its actions. Another limitation is that the client must implement all interface methods, and the methods are always called by the parser, regardless of whether the client is interested in them.

Microsoft recognized the state of parsers in the XML world and designed an efficient XML API that was also simple to use. Microsoft borrowed a concept from the "firehose" cursor used in ADO. The XmlReader abstract class describes an interface that provides a read-only, forward-only cursor model over the nodes in an XML document. It is called a "pull model" because the client pulls the data from the XmlReader a piece at a time and has control of moving the cursor along the document. The bottom part of Figure 1 contrasts the access methods of the XmlReader with those of the DOM and the SAX models.

XMLReader Navigation

The interface of XmlReader is more akin to an ADO recordset than the XML DOM. The XmlReader class has properties and methods that return the values and move the cursor across the document content. You can access value, node type, and namespace information quickly and easily using the properties shown in the following list.

  • Value
  • NodeType
  • LocalName
  • Prefix
  • NamespaceURI
  • Depth
  • EOF
  • HasAttributes
  • AttributeCount

A key thing to remember is that the XmlReader class has to be positioned on a node to read its values. In fact, to read the first node of the document, you must call the Read method to position it. Subsequent calls to the Read method move the cursor down the line in the document.

Because the XmlReader class is abstract, concrete derivative classes provide the actual functionality. Three main implementations are available to clients in the .NET framework: TextReader, NodeReader, and ValidatingReader. TextReader operates over a document that is in a serialized, string format. NodeReader operates over a set of nodes that have already been parsed in an XmlNode format used by the XmlDocument class, described in the previous article. ValidatingReader is based on the TextReader but adds an extra layer that does XML schema validation of the document being read.

We bring back the purchase order XML document from the previous example to illustrate how to use the XmlReader in Listing 1.

Listing 1: PO.xml

<?xml version="1.0" encoding="utf-8" ?>
<po:PurchaseOrder 
   xmlns:po="http://michalk.com/XmlDOM/PO.xsd" 
   xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <Number>1001</Number>
   <OrderDate>8/12/01</OrderDate>
   <BillToAddress>
     <Street>101 Main Street</Street>
     <City>Charlotte</City>
     <State>NC</State>
     <ZipCode>28273</ZipCode>
   </BillToAddress>
   <ShipToAddress>
     <Street>101 Main Street</Street>
     <City>Charlotte</City>
     <State>NC</State>
     <ZipCode>28273</ZipCode>
   </ShipToAddress>
   <LineItem Name="Computer Desk" Description="Wood desk for computer"
   SKU="12345A123" Price="499.99" Qty="1" />
</po:PurchaseOrder>

Our first crack at the XmlTextReader parsing shown in Listing 2 navigates through all the element nodes in the document. Element navigation is the default traversal of a document using the Read method. The loop that traverses the document uses the return value from Read to tell it when to break out of the loop. We could have used the EOF property to accomplish the same thing. The resulting output is shown in Listing 3.

Listing 2: XmlTextReader Default Navigation Code

using System;
using System.Xml;

namespace XmlDemos
{

public class ReaderNavDefault
{

public static void Main()
{
   // load the PO document 
   XmlTextReader reader = new XmlTextReader("PO.xml");

   // ignore the whitespace in the document
   reader.WhitespaceHandling = WhitespaceHandling.None;

   Console.WriteLine("Walking nodes in document..\n");

   // read each node in the document
   // using the default traversal path
   while (reader.Read())
   {
     // call routine for printing out spacing
     PrintDepth(reader.Depth);

   // display node information
   Console.WriteLine("Name:{0} Type:{1} Value:{2}",
   reader.Name, reader.NodeType, reader.Value);
}

}

public static void PrintDepth(int depth)
{
for (int i=0; i < depth; i++)
Console.Write("  ");
}

}
}

Listing 3: XmlTextReader Default Navigation Output

Walking nodes in document..

Name:xml Type:XmlDeclaration Value:version="1.0" encoding="utf-8"
Name:po:PurchaseOrder Type:Element Value:
  Name:Number Type:Element Value:
    Name: Type:Text Value:1001
  Name:Number Type:EndElement Value:
  Name:OrderDate Type:Element Value:
    Name: Type:Text Value:8/12/01
  Name:OrderDate Type:EndElement Value:
  Name:BillToAddress Type:Element Value:
    Name:Street Type:Element Value:
      Name: Type:Text Value:101 Main Street
    Name:Street Type:EndElement Value:
    Name:City Type:Element Value:
      Name: Type:Text Value:Charlotte
    Name:City Type:EndElement Value:
    Name:State Type:Element Value:
      Name: Type:Text Value:NC
    Name:State Type:EndElement Value:
    Name:ZipCode Type:Element Value:
      Name: Type:Text Value:28273
    Name:ZipCode Type:EndElement Value:
  Name:BillToAddress Type:EndElement Value:
  Name:ShipToAddress Type:Element Value:
    Name:Street Type:Element Value:
      Name: Type:Text Value:101 Main Street
    Name:Street Type:EndElement Value:
    Name:City Type:Element Value:
      Name: Type:Text Value:Charlotte
    Name:City Type:EndElement Value:
    Name:State Type:Element Value:
      Name: Type:Text Value:NC
    Name:State Type:EndElement Value:
    Name:ZipCode Type:Element Value:
      Name: Type:Text Value:28273
    Name:ZipCode Type:EndElement Value:
  Name:ShipToAddress Type:EndElement Value:
  Name:LineItem Type:Element Value:
Name:po:PurchaseOrder Type:EndElement Value:
  • + Share This
  • 🔖 Save To Your Account

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit 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 Peachpit 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 ask@peachpit.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 Adobe Press. 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.peachpit.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