Tài liệu Module 2: Parsing XML pptx

To teach this module, you need the following materials: Microsoft® PowerPoint® file 2663A_02.ppt 2663A_02_Code.htm To prepare to effectively teach this module: Read the following M

Contents

Overview 1

Lesson: Overview of XML Parsing 2

Lesson: Parsing XML Using XmlTextReader 14

Lesson: Creating a Custom Reader 31

Review 37

Module 2: Parsing XML

Information in this document, including URL and other Internet Web site references, is subject to change without notice Unless otherwise noted, the example companies, organizations, products, domain names, e-mail addresses, logos, people, places, and events depicted herein are fictitious, and no association with any real company, organization, product, domain name, e-mail address, logo, person, place or event is intended or should be inferred Complying with all applicable copyright laws is the responsibility of the user Without limiting the rights under copyright, no part

of this document may be reproduced, stored in or introduced into a retrieval system, or transmitted

in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of Microsoft Corporation

Microsoft may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document Except as expressly provided in any written license agreement from Microsoft, the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property

©2002 Microsoft Corporation All rights reserved

Microsoft, MS-DOS, Windows, Windows NT, Win32, Active Directory, ActiveX, BizTalk, IntelliSense, JScript, Microsoft Press, MSDN, PowerPoint, SQL Server, Visual Basic, Visual C#, and Visual Studio are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries

The names of actual companies and products mentioned herein may be the trademarks of their respective owners

Instructor Notes

After completing this module, students will be able to:

Create a Stream object from an XML file

Build a mutable string by using the StringBuilder object

Handle errors in the form of XML

Parse XML as text by using the XmlTextReader object

Create a custom XmlReader object

To teach this module, you need the following materials:

Microsoft® PowerPoint® file 2663A_02.ppt

2663A_02_Code.htm

To prepare to effectively teach this module:

Read the following Microsoft NET Framework Class Library topics:

• XmlReader Class

• XmlTextReader

• StringBuilder Class

Read all of the materials for this module

Complete the practices and the lab

Practice delivering the demonstrations

In this module, some of the Microsoft PowerPoint® slides provide hyperlinks that open a code samples page in the Web browser The code samples page provides a way to show and discuss code samples when there is not enough space for the code on the PowerPoint slide It also allows students to copy code samples directly from the browser window and paste them into a development environment All of the linked code samples for this module are in a single htm file

To open a code sample, click the appropriate hyperlink on the slide To navigate between code samples in a particular language, use the table of contents

provided at the top of the code page Each hyperlink opens a separate instance

the Web browser, so it is a good practice to click the Back button in Microsoft

Internet Explorer after viewing a code sample This will close the browser window and return you to the PowerPoint presentation

Required materials

Preparation tasks

Hyperlinked Code

Examples

How to Teach This Module

This section contains information that will help you to teach this module

Lesson: Overview of XML Parsing

This section describes the instructional methods for teaching each topic in this lesson

This topic introduces the module by defining the technical problem of parsing XML Most students will already understand what parsing is and why they would do it

This topic introduces XmlReader by comparing it with the Simple application

programming interface (API) for XML, or SAX, which many students are already familiar with Many students should also already be aware of the two models of XML parsing, the push model versus the pull model This topic compares SAX, as an example of the push model, to the Microsoft NET

Framework XmlReader class, as an example of the pull model of XML

processing As the lesson progresses, if you identify those students who have previous experience writing a SAX application, they might be able to help you

point out the advantages of XmlReader

Briefly cover the major features of the XmlReader class Students might ask about the technique of using XmlValidatingReader with a

ValidationEventHandler, which is covered in the next module

We cover reading XML from streams early, because it is a basic skill Be prepared to provide a definition of a stream

Another basic skill is creating and appending parsed XML by using a

StringBuilder object StringBuilder is preferred over the String object, because it uses much less memory StringBuilder also allows you to append content to the string without having to create a new StringBuilder object

Lesson: Parsing XML Using XmlTextReader

This section describes the instructional methods for teaching each topic in this lesson

This demonstration consists of showing typically usage of three functions of a Microsoft Visual Studio® NET add-in that was custom-built for this course To prepare for this demonstration, you should perform the demonstration steps as they are written and prepare to explain what the add-in does

Do not walk through the code during the demonstrations There are separate code examinations you will perform in which you will do just that

For more information about the add-in see Appendix A, “The XML Tools Add-In.”

Show how to instantiate a new XmlTextReader

Discuss the Read() method

How to Read Streams

How to Build Strings

Discuss the NodeType property

Discuss how to use the Name, Value, and Attributes properties to read the

To change the display options

1 On the Tools menu, click Options

2 Click the Text Editor folder, and then click the HTML/XML folder

3 Select the Word wrap and Line numbers options

While in the Code window, pressing CTRL+R twice will toggle word wrap on and off

4 Click the Environment folder, and then click the Fonts and Colors folder

5 Change the font used for the Text Editor and the Text Output Tool Windows to Lucida Console 14 pt

6 Click OK

7 Close and restart Visual Studio NET for the changes to take effect

Lesson: Creating a Custom Reader

This section describes the instructional methods for teaching each topic in this lesson

Be prepared to provide one or two anecdotes that illustrate the need for a custom reader

Discuss the types of XmlReader you can inherit from and the mechanics of overriding the Read() method

Be prepared to explain how the Read() method exposes the attribute as an element node type by using the XmlNodeType.Name and

XmlNodeType.Value properties

How to Determine the

Current Node Type

How to Read the

Overview

Overview of XML Parsing

Parsing XML Using XmlTextReader

Creating a Custom Reader

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

This module discusses how to parse Extensible Markup Language (XML) data

from a file, string, or stream by using the XmlTextReader class The XmlNodeReader object is not covered in this module, but works in a similar way as the XmlTextReader object

Both the XmlTextReader and XmlNodeReader objects inherit from XmlReader If these descendant objects do not provide the needed

functionality, you can create a custom reader object that inherits from

XmlReader

After completing this module, you will be able to use the Microsoft® NET Framework to:

Create a Stream object from an XML file

Build a mutable string by using the StringBuilder object

Handle errors in the form of XML

Parse XML as text by using the XmlTextReader object

Create a custom XmlReader object

Introduction

Objectives

Lesson: Overview of XML Parsing

Introduction to XML Parsing

XML Parsing Models

Parsing XML with the XmlReader Class

How to Read Streams

How to Build Strings from Parsed XML

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

The XmlReader base class and the objects that inherit from it are a powerful set of tools for parsing XML This lesson discusses how to use the XmlReader

and supporting classes to parse XML in a variety of use contexts

After completing this lesson, you will be able to:

Read XML from a File object

Read XML from a Stream object

Store XML in a StringBuilder object

Introduction

Lesson objectives

Introduction to XML Parsing

Parsing and reading XML mean the same thing

Parse XML to find content and to use node information

Create a list by node type

Sort nodes by namespace identifier

List all of the child elements in an XML source

Find a node by relative position

Find the last node to signal when to stop parsing

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

What does it mean to parse XML? Parsing refers to the process of reading

XML and then performing some action based on the information read

When you parse XML, you often filter the data in an attempt to locate a particular data value or range of values At other times, you might be more

interested in the node information that the parser finds The term node, when

used in this context, refers to a node as defined by the World Wide Web Consortium (W3C) XML Information Set Recommendation available at http://www.w3.org/TR/xml-infoset

Parsing XML allows you to query an XML source to find a particular data value For example, suppose that you must build an application that can query a local store of XML-based human resources data Parsing the XML should allow you to find a particular value such as the record that is associated with an employee number that is equal to “12345.”

Parsing also allows you to filter an XML source to find a set of related information For example, you might want to filter a personnel listing to find those employees whose hire date falls within the current month

Parsing allows you to use the node information in an XML source, such as the node type, or node value The following are useful tasks that you can

accomplish by using node information made available by parsing:

Use node information to create a list by node type

Sort nodes by namespace identifier

List all of the child elements in an XML source

Introduction

Find particular content

Make use of node

information

Application Generate calls to XmlReader that pull specific XML

SAX XML reader Push unfiltered XML to the calling application

XmlReader class

Pull specified XML and implement error handling

XmlReader class Pull specified XML and implement error handling

Application Process nodes, handle errors, and monitor the state of the reader

XmlTextReader

Content Handler Error Handler

XmlNodeReader

Node Handler

XmlValidatingReader

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

XML processors are based on the push model or the pull model of XML processing The push model is typified by a processor that uses the Simple application programming interface (API) for XML, referred to as SAX The pull model is typified by how the NET Framework XML reader classes process XML

The push model of XML processing means that the parser “pushes” to the

application an unfiltered, steady stream of parsed XML nodes SAX is an example of a parser that does this SAX pushes unfiltered XML nodes in response to a request by an application

You must write applications that consume unfiltered XML nodes to filter relevant node information and content The push model assumes that there is perfectly formed XML If the SAX processor finds an XML error, it

immediately stops processing and then sends an exception to the calling application You should write any application that uses the push model of XML processing to handle a variety of XML errors

SAX is not supported by the NET Framework, but you can use existing SAX tools, such as the Microsoft XML Parser (MSXML), in your NET-based programs

Introduction

What is the push model

of XML processing?

The pull model of XML processing means that the parser pulls from the XML

source only those nodes that it is instructed to pull by a calling application

XmlReader, a NET Framework class, is an example of a parser that pulls a

filtered set of XML nodes in response to a request by an application

XmlReader objects read the XML one node at a time and only send

notification to the application in response to some predefined criteria Similar to

the SAX processor, if an XmlReader object finds an XML error, it sends an exception to the calling application Unlike the SAX processor, XmlReader

objects are designed to continue processing XML even after an XML error is found

There are two main advantages of using the XmlReader pull model versus the

push model, when it is implemented by SAX First, it is easier to code

applications that use the XmlReader XmlReader pull-processing is typically

implemented by using looping structures, whereas push models use routines that handle state Looping structures are easier to write than routines that handle state Although contextual state management is still a challenge with the pull model, managing the context is easier to code by using consumer-driven procedural techniques

Second, applications that use XmlReader can potentially perform better

because they require less processing power and memory than applications that

rely on SAX Applications that use XmlReader can take advantage of client

hints to make more efficient use of character buffers; for example, by avoiding needless string copies Consumers can also selectively process elements; for example, by skipping elements of no interest and by not expanding entities With a push model, everything must be passed through the application, because the reader has no way of knowing what is important

If you still prefer to use a push model, you can layer a set of push-style

interfaces on top of the XmlReader pull model, but the reverse is not yet true

A sample SAX2 implementation layered over an XmlReader may ship with the

.NET Framework software development kit (SDK)

What is the pull model of

XML processing?

The following table summarizes the primary benefits of the pull model

Benefit Description

complex state machines The pull model client simplifies state management by means of a natural, top-down procedural refinement

input streams This task is extremely complicated in the push model

reverse is not true

parser writes a string object to its own buffer Then, the parser pushes the string object to the client buffer

In the pull model, the string is read into the parser buffer one time only

attributes, processing instructions, and white space The pull model client can skip items, processing only those items that are of interest to the application This allows for extremely efficient applications

Summary of pull model

benefits

Parsing XML with the XmlReader Class

What is XmlReader?

An abstract base class

Extends to these XML readers: XmlTextReader, XmlNodeReader, and XmlValidatingReader

Can be used either to create customized readers

Non-cached, forward-only, read-only access

Allows you to pull only those nodes that interest you

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

The XmlReader class is an abstract base class that provides non-cached,

forward-only, read-only access to XML sources, including streams, files, and Uniform Resource Locators (URLs) It implements the namespace requirements outlined in the Namespaces in XML Recommendation provided by the W3C, located at http://www.w3.org/TR/REC-xml-names/

XmlReader class objects can quickly read data from XML sources without

placing high demands on system resources such as memory and CPU time

Because XmlReader is an abstract base class, you can use it to create your own type of reader or implement one of the XmlReader extended classes The XmlReader class has three implementations that extend the base class and vary

in their design to support different scenario needs

The following table describes the implementations of the XmlReader class Class Description

XmlTextReader Reads character streams This is a forward-only reader

that has methods that return data on content and node types

XmlNodeReader Provides a parser over an XML Document Object Model

(DOM) API

XmlValidatingReader Provides a fully compliant validating or non-validating

XML parser with Document Type Definition (DTD), XML Schema Definition language (XSD) schema, or XML-Data Reduced (XDR) schema support This class

takes an XmlTextReader and layers validation services

By using the XmlReader class members, you can develop a solution that can

respond conditionally to node information in the XML source

XmlReader class objects read XML by stepping though it one node at a time

As each node is read, the program can perform actions based on the qualities of that node Such qualities include the type of the node, its attributes and data, and other node information

As an additional benefit to the job of programming, XmlReader class objects

determine if the XML is well-formed If the XML contains an error,

XmlReader objects throw an exception of the type XmlException, and the

processing stops

To continue processing after an error occurs, you must use an

XmlValidatingReader with a ValidationEventHandler instead

For a complete description of the members of the XmlReader class, see

XmlReader Members in the Additional Reading folder

To use an XmlReader object or any of its derived classes in your application, you must provide a reference to the NET Framework System.Xml

How to Read Streams

A stream is an abstraction of bytes drawn from any number of sources

A stream may be created from a file, URL, or another stream

Use a StreamReader to read a stream

object = new Stream( file | string | stream )

Visual Basic Example C# Example

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

Your application can use the classes contained in the System.IO namespace to

read XML data from a stream or from a file The terms file and stream convey a

particular meaning within the NET Framework

The term file is here used in the ordinary sense: an ordered and named

collection of a particular sequence of bytes having persistent storage When you program an application to read XML from a file, you must consider directory paths, disk storage, and file and directory names

To simplify the job of programming an application to read files, you can use NET Framework file and directory system input and output classes The

following table describes the file and directory System.IO classes

System.IO class Description File Provides static methods to create, copy, move, and open files Aids

in the creation of FileStream objects The FileInfo class provides

instance methods

Directory Provides static methods to create, move, and enumerate directories

and subdirectories The DirectoryInfo class provides instance

methods

TextReader Represents a reader that can read a sequential series of characters

TextReader is designed for character input, whereas the Stream

class is designed for byte input and output

StreamReader Implements a TextReader that reads characters from a byte stream

in a particular encoding StreamReader is designed for character input in a particular encoding, whereas the Stream class is

designed for byte input and output

Introduction

What is a file?

System.IO classes for

reading files

A stream is an abstraction of a sequence of bytes The bytes themselves can

originate from any number of sources, such as a file, an input/output device, an interprocess communication pipe, or a Transmission Control Protocol/Internet Protocol (TCP/IP) socket Examples of streams include network, memory, and tape streams

The Stream class and its derived classes provide a generic view of a sequence

of bytes Using a stream simplifies the job of programming read operations of XML that might originate from various operating systems and devices

Streams involve the following fundamental operations:

Streams can be read from Reading is the transfer of data from a stream into

a data structure, such as an array of bytes

Streams can be written to Writing is the transfer of data from a data structure into a stream

Streams can support seeking Seeking is the querying and modifying of the current position within a stream

Depending on the underlying data source or repository, streams might support only some of these capabilities

What is a stream?

In this example, a StreamReader object is created from a File object The

following code example, provided in both the Microsoft Visual Basic® and C# languages, reads an entire text file line by line

All code samples assume that any required namespaces are aliased at the

top of the class For example, to use the classes within the System.IO

namespace, the following statement is required:

' Visual Basic ® Imports System.IO // C#

using System.IO;

' Visual Basic Dim BooksFilename As String = "c:\books.txt"

If File.Exists(BooksFilename) Then Dim BooksReader As StreamReader = _ File.OpenText(BooksFilename) Dim CurrentLine As String = BooksReader.ReadLine() While Not CurrentLine Is Nothing

' process line CurrentLine = BooksReader.ReadLine() End While

BooksReader.Close() End If

// C#

string BooksFilename = @"c:\books.txt";

if (File.Exists(BooksFilename)) { StreamReader BooksReader = File.OpenText(BooksFilename); String CurrentLine = BooksReader.ReadLine();

while (CurrentLine != null) { // process line

CurrentLine = BooksReader.ReadLine();

} BooksReader.Close();

} For more information, search the NET Framework Class Library for the

keywords Stream Class

When using the classes in the System.IO namespace, you must satisfy the

operating system security requirements, such as access control lists (ACLs), for

access to be allowed This requirement is in addition to any FileIOPermission

How to Build Strings from Parsed XML

The String object is immutable

Do NOT use when concatenating in a loop

The StringBuilder object is mutable

To build a string with the StringBuilder class, use the Append() method inside a loop

Use the ToString() method to retrieve the string

Visual Basic Example C# Example

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

It is typical for an application that reads XML to build strings to hold filtered data A reader object is normally inserted into a looping structure In such a case, each time the loop iterates, the reader object reads another node or set of nodes and then copies the data into a string object For a large XML file, the loop might iterate thousands of times and build a result composed of tens of thousands of XML nodes

When you want to modify a string without creating a new object, consider using

the System.Text.StringBuilder class instead of the String class For example, using the StringBuilder class can boost performance when concatenating many

strings together in a loop

The System.Text.StringBuilder class represents a mutable string of characters This means that you can modify the contents of a StringBuilder object The

value is said to be mutable because it can be modified after it has been created,

by appending, removing, replacing, or inserting characters

At first glance, you might decide to try the String class as the object type

to concatenate XML fragments that originate from an XML reader However,

this would be a mistake, because the String class is designed to represent an

immutable series of characters This means that you cannot simply append new

characters to a String class each time a reader iterates through a looping structure Doing so creates multiple instances of the String object and can

easily result in highly expensive XML source processing However, in the case

of reading a file into a stream, an appropriate first step is to load the file into a

String object The stream can then load the XML from the String object

Introduction

What is the

StringBuilder class?

Note

The following example initializes a new instance of the StringBuilder class by

using the specified string, and then creates a string containing the 12 Times

Table by using a for loop:

' Visual Basic Dim sb As New StringBuilder("12 Times Table:") Dim i As Integer

For i = 1 To 12 sb.Append(vbCrLf & i & " x 12 = " & i * 12) Next

MessageBox.Show(sb.ToString()) ' Do NOT use the String class, for example Dim s As String = "12 Times Table:"

Dim i As Integer For i = 1 To 12

s += vbCrLf & i & " x 12 = " & i * 12 Next

MessageBox.Show(s) // C#

StringBuilder sb = new StringBuilder("12 Times Table:"); for (int i = 1; i <= 12; i++) {

sb.Append("\n" + i + " x 12 = " + i * 12);

} MessageBox.Show(sb.ToString());

// Do NOT use the String class, for example string s = "12 Times Table:";

for (int i = 1; i <= 12; i++) {

s += "\n" + i + " x 12 = " + i * 12;

} MessageBox.Show(s);

Example

Lesson: Parsing XML Using XmlTextReader

Demonstration: Parsing XML

How to Create an XmlTextReader Object

How to Navigate Nodes

How to Determine the Current Node Type

How to Read the Contents of a Node

How to Handle White Space

How to Handle XML Errors While Parsing

Code Examination: Parsing XML

Practice: Reading XML Content and Nodes

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

The node information in an XML source is an important resource that you can use in applications that process XML You can use node information not only to find particular content, but also as a very useful basis for the logic that controls program flow In this lesson, you will learn how to find and use XML node information in your applications

After completing this lesson, you will be able to:

Navigate through XML nodes by using the Read() methods

Determine the current node type and extract information about the current node

Read the attributes of an element type of node

Handle white space in an XML document

Implement XML error handling while parsing

Introduction

Lesson objectives

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

In this demonstration, you will see the parsing and filtering functionality of the

XML Tools add-in Compiled release versions of the add-in written in both

Microsoft Visual C#™ and Microsoft Visual Basic® languages are available in the following folders:

install_folder\Democode\Addins\

XmlToolsAddinCS\XmlToolsAddinCSSetup\Release\

install_folder\Democode\Addins\

XmlToolsAddinVB\XmlToolsAddinVBSetup\Release\

To install the add-in

1 Double-click the setup.exe file in one of the folders above

2 Follow the instructions in the wizard

For detailed installation instructions see Appendix A

To parse a sample XML file that is open in the editor

1 In Microsoft Visual Studio® NET, open the files named books.xml and employee.xml These are located in the folder

</employees>

3 On the XML Tools toolbar, click Parse

Introduction

Demonstration

4 Notice that the Output window opens, showing detailed information about the employee.xml file Each node in the XML file appears as a row in the details table, and a count of the number of each type of node appears in the summary table

To parse another sample XML file

1 Click Solution Explorer to make it active

2 On the XML Tools toolbar, click Parse Because no XML file is active, a

dialog box appears prompting the user to choose one of the open files

3 In the Parse dialog box, click the file named books.xml, and then click OK

The Output window opens showing detailed information about the file

4 Use the Output window to verify the answers provided to the following questions:

a What is the Depth of the Text node with a value of Benjamin?

To parse a sample XML file in the internal browser

1 On the View menu, click Web Browser, and then click Show Browser (or press Ctrl+Alt+R)

2 Make sure that Set web links to internally or externally opened is set to

internal (The icon should look like this )

3 Enter the following URL in the Web toolbar:

http://localhost/2663/Democode/Mod02/books.xml

4 On the XML Tools toolbar, click Parse This demonstrates that the add-in

can parse any XML-compliant file that is accessible on the Internet

To filter by specifying a child element value

1 On the XML Tools toolbar, click Filter

2 If the add-in prompts to select a file, click books.xml, and then click OK

3 In the Filter dialog box, enter the following options, and then click OK Option Value

4 Notice that the Output window shows the one book that matches the filter

To filter by specifying an attribute value

1 On the XML Tools toolbar, click Filter

2 If the add-in prompts you to select a file, click books.xml, and then click

OK

3 In the Filter dialog box, enter the following options, and then click OK Option Value

4 Notice that the Output window shows the two books that match the filter

To convert the active file and save the result to a file

1 On the XML Tools toolbar, click Convert

2 If the add-in prompts to select a file, click books.xml, and then click OK

The Output window shows books.xml with all of its attributes converted to elements

3 Click the Output window to make it active, and then on the File menu, click Save Output As

4 Save the output as BooksAsElements.xml in the folder

install_folder\Democode\Mod02\

How to Create an XmlTextReader Object

XmlTextReader BooksReader =new XmlTextReader(@"c:\books.xml");

XmlTextReader BooksReader =new XmlTextReader(@"c:\books.xml");

Stream String TextReader URL

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

The XmlTextReader class is an implementation of XmlReader and provides a

high performance parser It enforces the rule that XML must be well-formed It

is neither a validating nor a non-validating parser, because it does not have DTD or schema information It can read text in blocks or read characters from a stream

The XmlTextReader can read data from different inputs

XmlTextReader BooksReader = new XmlTextReader(@"c:\books.xml");

Introduction

XmlTextReader

constructor