XML解析简介及Xerces-C++简单使用举例
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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