教你如何疾速从一个XML文件中查找信息的细致引见【XML教程】,XML，查找信息，文件

在网络时代,xml文件起到了一个保留和传输数据的作用。Soap协定经由过程Xml交流信息，数据库经由过程Xml文件存取等等。那末如何疾速的从一个XML文件中获得所需的信息呢？

我们晓得，java的JAXP中和Microsoft.Net都有Xml剖析器，Microsoft.Net是边读边剖析，而JAXP是读到内存中然后才举行剖析（另有一种是事宜机制去读），总而言之，是不利于疾速读取。基于此，Microsoft.Net 和JAXP都供应了XPATH机制，来疾速定位到XML文件中所需的节点。

比方有一个XML文件：booksort.xml:

<?xml version="1.0"?>

<!-- a fragment of a book store inventory database -->

<bookstore xmlns:bk="urn:samples">

<book genre="novel" publicationdate="1997" bk:ISBN="1-861001-57-8">

<title>PRide And Prejudice</title>

<author>

<first-name>Jane</first-name>

<last-name>Austen</last-name>

</author>

<price>24.95</price>

</book>

<book genre="novel" publicationdate="1992" bk:ISBN="1-861002-30-1">

<title>The Handmaid's Tale</title>

<author>

<first-name>Margaret</first-name>

<last-name>Atwood</last-name>

</author>

<price>29.95</price>

</book>

<book genre="novel" publicationdate="1991" bk:ISBN="1-861001-57-6">

<title>Emma</title>

<author>

<first-name>Jane</first-name>

<last-name>Austen</last-name>

</author>

<price>19.95</price>

</book>

<book genre="novel" publicationdate="1982" bk:ISBN="1-861001-45-3">

<title>Sense and Sensibility</title>

<author>

<first-name>Jane</first-name>

<last-name>Austen</last-name>

</author>

<price>19.95</price>

</book>

</bookstore>

假如我们想疾速查找”last-name”即是”Austen”的一切标落款，能够经由过程以下要领能够获得：

XmlReaderSample.cs

//Corelib.net/System.Xml.Xsl/XPathDocument Class

//Author :Any 


using System;

using System.IO;

using System.Xml;

using System.Xml.XPath;


public class XmlReaderSample

{

public static void Main()

{

XmlTextReader myxtreader = new XmlTextReader("booksort.xml");

XmlReader myxreader = myxtreader;

XPathDocument doc = new XPathDocument(myxreader);

XPathNavigator nav = doc.CreateNavigator();


XPathExpression expr; 

expr = nav.Compile("descendant::book[author/last-name='Austen']");


//expr.AddSort("title", XmlSortOrder.Ascending, XmlCaSEOrder.None, "", XmlDataType.Text);


XPathNodeIterator iterator = nav.Select(expr);

while (iterator.MoveNext())

{

XPathNavigator nav2 = iterator.Current;

nav2.MoveToFirstChild();

Console.WriteLine("Book title: {0}", nav2.Value);

}

}

}

运转这个顺序，效果为：

Book title: Pride And Prejudice

Book title: Emma

Book title: Sense and Sensibility

能够看到查找准确。

应用XPATH中的一些功用，也能够完成简朴的排序和简朴运算。如在数据库中常常要对数据举行汇总，就可用XPATH完成。

如：

order.xml

<!--Represents a customer order-->

<order>

<book ISBN='10-861003-324'>

<title>The Handmaid's Tale</title>

<price>19.95</price>

</book>

<cd ISBN='2-3631-4'>

<title>Americana</title>

<price>16.95</price>

</cd>

</order>

和：books.xml

<?xml version="1.0"?>

<!-- This file represents a fragment of a book store inventory database -->

<bookstore>

<book cc="dd" xmlns:bk="urn:sample" xmlns:ns="http://www.Any.com" genre="autobiography" publicationdate="1981" ISBN="1-861003-11-0">

<title>The Autobiography of Benjamin Franklin</title>

<ns:author>

<first-name>Benjamin</first-name>

<last-name>Franklin</last-name>

</ns:author>

<price>8.99</price>

</book>

<book genre="novel" publicationdate="1967" ISBN="0-201-63361-2">

<title>The Confidence Man</title>

<author>

<first-name>Herman</first-name>

<last-name>Melville</last-name>

</author>

<price>11.99</price>

</book>

<book genre="philosophy" publicationdate="1991" ISBN="1-861001-57-6">

<title>The Gorgias</title>

<author>

<name>Plato</name>

</author>

<price>9.99</price>

</book>

</bookstore>

我们能够对该XML文件中的price乞降，以获得价钱总数。

Evaluate.cs

//Corelib.net/System.Xml.Xsl/XPathNavigator Class

//Author :Any 


using System;

using System.IO;

using System.Xml;

using System.Xml.XPath;



public class EvaluateSample

{

public static void Main()

{

EvaluateSample myEvaluateSample = new EvaluateSample();

myEvaluateSample.test("books.xml");

}


public void test(String args)

{

try

{

//test Evaluate(String);

XPathDocument myXPathDocument = new XPathDocument(args);

XPathNavigator myXPathNavigator = myXPathDocument.CreateNavigator();

Console.WriteLine(myXPathNavigator.Evaluate("sum(descendant::book/price)"));


//testEvaluate(XPathExpression);

XmlDocument doc = new XmlDocument();

doc.Load("order.xml");

XPathNavigator nav = doc.CreateNavigator();

XPathExpression expr = nav.Compile("sum(//price/text())");

Console.WriteLine(nav.Evaluate(expr));


//testEvaluate(XPathExpression);


XPathNodeIterator myXPathNodeIterator = nav.Select("descendant::book/title");

expr = nav.Compile("sum(//price/text())");

Console.WriteLine(nav.Evaluate(expr,myXPathNodeIterator));


} 

catch (Exception e)

{

Console.WriteLine ("Exception: {0}", e.ToString());

}

}


}

运转这个顺序，效果以下：