使用XPath的步骤
以下是使用XPath解析器在解析文档时使用的步骤。
- 导入XML相关的软件包。
- 创建DocumentBuilder
- 从文件或数据流创建一个文档
- 创建XPath对象和XPath的路径表达式
- 编译XPath表达式使用XPath.compile() ,并由XPath.evaluate()评估计算获得一个节点列表
- 遍历节点列表。
- 检查属性
- 检查子元素
导入XML相关的软件包
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| import org.w3c.dom.*; import org.xml.sax.*; import javax.xml.parsers.*; import javax.xml.xpath.*; import java.io.*;
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创建DocumentBuilder
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| DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder();
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从文件或数据流创建一个文档
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| StringBuilder xmlStringBuilder = new StringBuilder(); xmlStringBuilder.append("<?xml version="1.0"?> <class> </class>"); ByteArrayInputStream input = new ByteArrayInputStream( xmlStringBuilder.toString().getBytes("UTF-8")); Document doc = builder.parse(input);
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构建XPath
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| XPath xPath = XPathFactory.newInstance().newXPath();
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准备路径表达式,并计算它
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| String expression = "/class/student"; NodeList nodeList = (NodeList) xPath.compile(expression).evaluate(doc, XPathConstants.NODESET);
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遍历节点列表
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| for (int i = 0; i < nodeList.getLength(); i++) { Node nNode = nodeList.item(i); ... }
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检查属性
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| //returns specific attribute getAttribute("attributeName"); //returns a Map (table) of names/values getAttributes();
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检查子元素
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| //returns a list of subelements of specified name getElementsByTagName("subelementName"); //returns a list of all child nodes getChildNodes();
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演示示例:
这里是我们需要分析输入文本文件:
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| <?xml version="1.0"?> <class> <student rollno="393"> <firstname>dinkar</firstname> <lastname>kad</lastname> <nickname>dinkar</nickname> <marks>85</marks> </student> <student rollno="493"> <firstname>Vaneet</firstname> <lastname>Gupta</lastname> <nickname>vinni</nickname> <marks>95</marks> </student> <student rollno="593"> <firstname>jasvir</firstname> <lastname>singh</lastname> <nickname>jazz</nickname> <marks>90</marks> </student> </class>
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演示示例:
XPathParserDemo.java
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| package com.yiibai.xml;
import java.io.File; import java.io.IOException;
import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.ParserConfigurationException; import javax.xml.xpath.XPath; import javax.xml.xpath.XPathConstants; import javax.xml.xpath.XPathExpressionException; import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document; import org.w3c.dom.NodeList; import org.w3c.dom.Node; import org.w3c.dom.Element; import org.xml.sax.SAXException;
public class XPathParserDemo { public static void main(String[] args) { try { File inputFile = new File("input.txt"); DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance(); DocumentBuilder dBuilder;
dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(inputFile); doc.getDocumentElement().normalize();
XPath xPath = XPathFactory.newInstance().newXPath();
String expression = "/class/student"; NodeList nodeList = (NodeList) xPath.compile(expression).evaluate(doc, XPathConstants.NODESET); for (int i = 0; i < nodeList.getLength(); i++) { Node nNode = nodeList.item(i); System.out.println("\nCurrent Element :" + nNode.getNodeName()); if (nNode.getNodeType() == Node.ELEMENT_NODE) { Element eElement = (Element) nNode; System.out.println("Student roll no : " + eElement.getAttribute("rollno")); System.out.println("First Name : " + eElement .getElementsByTagName("firstname") .item(0) .getTextContent()); System.out.println("Last Name : " + eElement .getElementsByTagName("lastname") .item(0) .getTextContent()); System.out.println("Nick Name : " + eElement .getElementsByTagName("nickname") .item(0) .getTextContent()); System.out.println("Marks : " + eElement .getElementsByTagName("marks") .item(0) .getTextContent()); } } } catch (ParserConfigurationException e) { e.printStackTrace(); } catch (SAXException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } catch (XPathExpressionException e) { e.printStackTrace(); } } }
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这将产生以下结果:
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| Current Element :student Student roll no : 393 First Name : dinkar Last Name : kad Nick Name : dinkar Marks : 85
Current Element :student Student roll no : 493 First Name : Vaneet Last Name : Gupta Nick Name : vinni Marks : 95
Current Element :student Student roll no : 593 First Name : jasvir Last Name : singh Nick Name : jazz Marks : 90
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