XML解析简介及Xerces-C++简单使用举例

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XML是由World WideWeb联盟(W3C)定义的元语言。它已经成为一种通用的数据交换格式,它的平台无关性,语言无关性,系统无关性,给数据集成与交互带来了极大的方便。XML在不同的语言里解析方式都是一样的,只不过实现的语法不同而已。

XML本身只是以纯文本对数据进行编码的一种格式,要想利用XML,或者说利用XML文件中所编码的数据,必须先将数据从纯文本中解析出来,因此,必须有一个能够识别XML文档中信息的解析器,用来解释XML文档并提取其中的数据。然而,根据数据提取的不同需求,又存在着多种解析方式,不同的解析方式有着各自的优缺点和适用环境。选择合适的XML解析技术能够有效提升应用系统的整体性能

所有的XML处理都从解析开始,无论是使用XSLT或Java语言,第一步都是要读入XML文件,解码结构和检索信息等等,这就是解析,即把代表XML文档的一个无结构的字符序列转换为满足XML语法的结构化组件的过程。

XML基本的的解析方式主要有两种:SAX(Simple API for XML)和DOM(Document ObjectModel)。

SAX是基于事件流的解析。SAX处理的优点非常类似于流媒体的优点。分析能够立即开始,而不是等待所有的数据被处理。而且,由于应用程序只是在读取数据时检查数据,因此不需要将数据存储在内存中。这对于大型文档来说是个巨大的优点。事实上,应用程序甚至不必解析整个文档,它可以在某个条件得到满足时停止解析。一般来说,SAX还比它的替代者DOM快很多。SAX解析器采用了基于事件的模型,它在解析XML文档的时候可以触发一系列的事件,当发现给定的tag的时候,它可以激活一个回调方法,告诉该方法制定的标签已经找到。SAX对内存的要求通常会比较低,因为它让开发人员来决定所要处理的tag。特别是当开发人员只需要处理文档中所包含的部分数据时,SAX这种扩展能力得到了更好的体现。但用SAX解析器的时候编码工作会比较困难,而且很难同时访问同一个文档中的多处不同数据。优点:(1)、不需要等待所有数据都被处理,分析就能立即开始;(2)、只在读取数据时检查数据,不需要保存在内存中;(3)、可以在某个条件得到满足时停止解析,不必解析整个文档;(4)、效率和性能较高,能解析大于系统内存的文档。缺点:(1)、需要应用程序自己负责TAG的处理逻辑(例如维护父/子关系等),文档越复杂程序就越复杂;(2)、单向导航,无法定位文档层次,很难同时访问同一文档的不同部分数据,不支持XPath。

DOM是用与平台和语言无关的方式表示XML文档的官方W3C标准。DOM是以层次结构组织的节点或信息片段的集合。这个层次结构允许开发人员在树中寻找特定信息。分析该结构通常需要加载整个文档和构造层次结构,然后才能做任何工作。由于它是基于信息层次的,因而DOM被认为是基于树或基于对象的。优点:(1)、允许应用程序对数据和结构做出更改;(2)、访问是双向的,可以在任何时候在树中上下导航,获取和操作任意部分的数据。缺点:通常需要加载整个XML文档来构造层次结构,消耗资源大。

基于C/C++语言的XML解析库包括

(1)、Expat:http://www.libexpat.org/

(2)、die-xml:https://code.google.com/p/die-xml/

(3)、Xerces-C++:http://xerces.apache.org/xerces-c/index.html

(4)、TinyXml:http://www.grinninglizard.com/tinyxml/

Xerces-C++的编译和使用:

1、 从http://xerces.apache.org/xerces-c/download.cgi#verify下载 xerces-c-3.1.1.zip 源代码,并解压缩;

2、 用vs2010打开xerces-c-3.1.1\projects\Win32\VC10\xerces-all目录下的xerces-all.sln;

3、 分别选择SolutionConfigurations、Solution Platforms中相关项,然后选中Solution ‘xerces-all’,-->单击右键,选择执行Rebuild Solution,会在/Build/Win32/VC10目录下生成相应的动态库和静态库,这里选择Static Debug/xerces-c_static_3D.lib和Static Release/xerces-c_static_3.lib进行测试;

4、在’xerces-all’工作空间的基础上新建一个TestXerces工程,选中此工程,分别在Debug和Release下,工程属性(1)、Configuration Properties -->Character Set:Use Unicode Character Set; (2)、C/C++-->General-->Additional Include Directories: ../../../../../src ,C/C++ -->Prerocessor中加入:
_CRT_SECURE_NO_DEPRECATE
_WINDOWS
XERCES_STATIC_LIBRARY
XERCES_BUILDING_LIBRARY
XERCES_USE_TRANSCODER_WINDOWS
XERCES_USE_MSGLOADER_INMEMORY
XERCES_USE_NETACCESSOR_WINSOCK
XERCES_USE_FILEMGR_WINDOWS
XERCES_USE_MUTEXMGR_WINDOWS
XERCES_PATH_DELIMITER_BACKSLASH
HAVE_STRICMP
HAVE_STRNICMP
HAVE_LIMITS_H
HAVE_SYS_TIMEB_H
HAVE_FTIME
HAVE_WCSUPR
HAVE_WCSLWR
HAVE_WCSICMP
HAVE_WCSNICMP

stdafx.h:
#pragma once

#include "targetver.h"

#include <stdio.h>

#include "xercesc/util/PlatformUtils.hpp"
#include "xercesc/util/XMLString.hpp"
#include "xercesc/dom/DOM.hpp"
#include "xercesc/util/OutOfMemoryException.hpp"
#include "xercesc/util/TransService.hpp"
#include "xercesc/parsers/SAXParser.hpp"
#include "xercesc/sax/HandlerBase.hpp"
#include "xercesc/framework/XMLFormatter.hpp"

stdafx.cpp:
#include "stdafx.h"

// TODO: reference any additional headers you need in STDAFX.H
// and not in this file
#ifdef _DEBUG
	#pragma comment(lib,"../../../../../Build/Win32/VC10/Static Debug/xerces-c_static_3D.lib") 
#else
	#pragma comment(lib,"../../../../../Build/Win32/VC10/Static Release/xerces-c_static_3.lib") 
#endif

TestXerces.cpp:
#include "stdafx.h"
#include <iostream>

using namespace std;

XERCES_CPP_NAMESPACE_USE

class XStr
{
public :
	// -----------------------------------------------------------------------
	//  Constructors and Destructor
	// -----------------------------------------------------------------------
	XStr(const char* const toTranscode)
	{
		// Call the private transcoding method
		fUnicodeForm = XMLString::transcode(toTranscode);
	}

	~XStr()
	{
		XMLString::release(&fUnicodeForm);
	}

	// -----------------------------------------------------------------------
	//  Getter methods
	// -----------------------------------------------------------------------
	const XMLCh* unicodeForm() const
	{
		return fUnicodeForm;
	}

private :
	// -----------------------------------------------------------------------
	//  Private data members
	//
	//  fUnicodeForm
	//      This is the Unicode XMLCh format of the string.
	// -----------------------------------------------------------------------
	XMLCh*   fUnicodeForm;
};

#define X(str) XStr(str).unicodeForm()

/*
* This sample illustrates how you can create a DOM tree in memory.
* It then prints the count of elements in the tree.
*/
int CreateDOMDocument()
{
	// Initialize the XML4C2 system.
	try {
		XMLPlatformUtils::Initialize();
	} catch(const XMLException& toCatch) {
		char *pMsg = XMLString::transcode(toCatch.getMessage());
		XERCES_STD_QUALIFIER cerr << "Error during Xerces-c Initialization.\n"
			<< "  Exception message:"
			<< pMsg;
		XMLString::release(&pMsg);
		return 1;
	}

	// Watch for special case help request
	int errorCode = 0;

	/*{
	XERCES_STD_QUALIFIER cout << "\nUsage:\n"
	"    CreateDOMDocument\n\n"
	"This program creates a new DOM document from scratch in memory.\n"
	"It then prints the count of elements in the tree.\n"
	<< XERCES_STD_QUALIFIER endl;
	errorCode = 1;
	}*/
	if(errorCode) {
		XMLPlatformUtils::Terminate();
		return errorCode;
	}

	{
		//  Nest entire test in an inner block.
		//  The tree we create below is the same that the XercesDOMParser would
		//  have created,except that no whitespace text nodes would be created.

		// <company>
		//     <product>Xerces-C</product>
		//     <category idea='great'>XML Parsing Tools</category>
		//     <developedBy>Apache Software Foundation</developedBy>
		// </company>
		DOMImplementation* impl =  DOMImplementationRegistry::getDOMImplementation(X("Core"));

		if (impl != NULL) {
			try {
				DOMDocument* doc = impl->createDocument(
					0,// root element namespace URI.
					X("company"),// root element name
					0);                   // document type object (DTD).

				DOMElement* rootElem = doc->getDocumentElement();

				DOMElement*  prodElem = doc->createElement(X("product"));
				rootElem->appendChild(prodElem);

				DOMText*    prodDataVal = doc->createTextNode(X("Xerces-C"));
				prodElem->appendChild(prodDataVal);

				DOMElement*  catElem = doc->createElement(X("category"));
				rootElem->appendChild(catElem);

				catElem->setAttribute(X("idea"),X("great"));

				DOMText*    catDataVal = doc->createTextNode(X("XML Parsing Tools"));
				catElem->appendChild(catDataVal);

				DOMElement*  devByElem = doc->createElement(X("developedBy"));
				rootElem->appendChild(devByElem);

				DOMText*    devByDataVal = doc->createTextNode(X("Apache Software Foundation"));
				devByElem->appendChild(devByDataVal);

				//
				// Now count the number of elements in the above DOM tree.
				//
				const XMLSize_t elementCount = doc->getElementsByTagName(X("*"))->getLength();
				XERCES_STD_QUALIFIER cout << "The tree just created contains: " << elementCount
					<< " elements." << XERCES_STD_QUALIFIER endl;

				doc->release();
			} catch (const OutOfMemoryException&) {
				XERCES_STD_QUALIFIER cerr << "OutOfMemoryException" << XERCES_STD_QUALIFIER endl;
				errorCode = 5;
			} catch (const DOMException& e) {
				XERCES_STD_QUALIFIER cerr << "DOMException code is:  " << e.code << XERCES_STD_QUALIFIER endl;
				errorCode = 2;
			} catch (...) {
				XERCES_STD_QUALIFIER cerr << "An error occurred creating the document" << XERCES_STD_QUALIFIER endl;
				errorCode = 3;
			}
		} else{// (inpl != NULL)
			XERCES_STD_QUALIFIER cerr << "Requested implementation is not supported" << XERCES_STD_QUALIFIER endl;
			errorCode = 4;
		}
	}

	XMLPlatformUtils::Terminate();
	return errorCode;
}


// ---------------------------------------------------------------------------
//  This is a simple class that lets us do easy (though not terribly efficient)
//  transcoding of XMLCh data to local code page for display.
// ---------------------------------------------------------------------------
class StrX
{
public :
	// -----------------------------------------------------------------------
	//  Constructors and Destructor
	// -----------------------------------------------------------------------
	StrX(const XMLCh* const toTranscode)
	{
		// Call the private transcoding method
		fLocalForm = XMLString::transcode(toTranscode);
	}

	~StrX()
	{
		XMLString::release(&fLocalForm);
	}

	// -----------------------------------------------------------------------
	//  Getter methods
	// -----------------------------------------------------------------------
	const char* localForm() const
	{
		return fLocalForm;
	}

private :
	// -----------------------------------------------------------------------
	//  Private data members
	//
	//  fLocalForm
	//      This is the local code page form of the string.
	// -----------------------------------------------------------------------
	char*   fLocalForm;
};

inline XERCES_STD_QUALIFIER ostream& operator<<(XERCES_STD_QUALIFIER ostream& target,const StrX& toDump)
{
	target << toDump.localForm();
	return target;
}

int SAXPrint()
{
	// ---------------------------------------------------------------------------
	//  Local data
	//
	//  doNamespaces
	//      Indicates whether namespace processing should be enabled or not.
	//      Defaults to disabled.
	//
	//  doSchema
	//      Indicates whether schema processing should be enabled or not.
	//      Defaults to disabled.
	//
	//  schemaFullChecking
	//      Indicates whether full schema constraint checking should be enabled or not.
	//      Defaults to disabled.
	//
	//  encodingName
	//      The encoding we are to output in. If not set on the command line,//      then it is defaulted to LATIN1.
	//
	//  xmlFile
	//      The path to the file to parser. Set via command line.
	//
	//  valScheme
	//      Indicates what validation scheme to use. It defaults to 'auto',but
	//      can be set via the -v= command.
	// ---------------------------------------------------------------------------
	static bool                     doNamespaces        = false;
	static bool                     doSchema            = false;
	static bool                     schemaFullChecking  = false;
	static const char*              encodingName    = "LATIN1";
	static XMLFormatter::UnRepFlags unRepFlags      = XMLFormatter::UnRep_CharRef;
	static char*                    xmlFile         = 0;
	static SAXParser::ValSchemes    valScheme       = SAXParser::Val_Auto;

	// Initialize the XML4C2 system
	try {
		XMLPlatformUtils::Initialize();
	} catch (const XMLException& toCatch) {
		XERCES_STD_QUALIFIER cerr << "Error during initialization! :\n"
			<< StrX(toCatch.getMessage()) << XERCES_STD_QUALIFIER endl;
		return 1;
	}

	xmlFile = "../../../../../samples/data/personal-schema.xml";
	int errorCount = 0;

	//
	//  Create a SAX parser object. Then,according to what we were told on
	//  the command line,set it to validate or not.
	//
	SAXParser* parser = new SAXParser;
	parser->setValidationScheme(valScheme);
	parser->setDoNamespaces(doNamespaces);
	parser->setDoSchema(doSchema);
	parser->setHandleMultipleImports (true);
	parser->setValidationSchemaFullChecking(schemaFullChecking);

	//
	//  Create the handler object and install it as the document and error
	//  handler for the parser-> Then parse the file and catch any exceptions
	//  that propogate out
	//
	int errorCode = 0;
	try {
		//SAXPrintHandlers handler(encodingName,unRepFlags);
		//parser->setDocumentHandler(&handler);
		//parser->setErrorHandler(&handler);
		parser->parse(xmlFile);
		errorCount = parser->getErrorCount();
	} catch (const OutOfMemoryException&) {
		XERCES_STD_QUALIFIER cerr << "OutOfMemoryException" << XERCES_STD_QUALIFIER endl;
		errorCode = 5;
	} catch (const XMLException& toCatch) {
		XERCES_STD_QUALIFIER cerr << "\nAn error occurred\n  Error: "
			<< StrX(toCatch.getMessage())
			<< "\n" << XERCES_STD_QUALIFIER endl;
		errorCode = 4;
	}

	if(errorCode) {
		XMLPlatformUtils::Terminate();
		return errorCode;
	}

	//
	//  Delete the parser itself.  Must be done prior to calling Terminate,below.
	//
	delete parser;

	// And call the termination method
	XMLPlatformUtils::Terminate();

	if (errorCount > 0)
		return 4;
	else
		return 0;

	return 0;
}

int main(int argc,char* argv[])
{
	CreateDOMDocument();

	SAXPrint();

	cout<<"ok!"<<endl;

	return 0;
}
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