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:
30.97 36.9 36.9
我们能够看到,30.97是books.xml中一切price值的总和,而36.9则是order.xml中一切price值的总和。经由过程XPAH不仅能够疾速查找信息,而且还能够对信息举行一些基础的处置惩罚。
以上就是教你如何疾速从一个XML文件中查找信息的细致引见的内容,更多相关内容请关注ki4网(www.ki4.cn)!