XPath JAVA用法总结及代码样例

一、基本概念介绍

    XPath 是一门在 XML 文档中查找信息的语言， 可用来在 XML 文档中对元素和属性进行遍历。XPath 是 W3C XSLT 标准的主要元素，并且 XQuery 和 XPointer 同时被构建于 XPath 表达之上。因此，对 XPath 的理解是很多高级 XML 应用的基础。
    XPath非常类似对数据库操作的SQL语言，或者说JQuery，它可以方便开发者抓起文档中需要的东西。（dom4j也支持xpath

   1.节点类型

    XPath中有七种结点类型：元素、属性、文本、命名空间、处理指令、注释以及文档节点（或称为根节点）。文档中存在元素节点，属性节点，根节点

   2.常用路径表达式

  
示例如下：

 3.限定语

用来查找某个特定的节点或者包含某个指定的值的节点。以方括号括起

4 .通配符

二、代码示例

import java.io.File;
import java.io.FileInputStream;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
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.Node;
import org.w3c.dom.NodeList;

public class XPathDemo {
	private static Document doc;
	private static XPath xpath;

	public static void main(String[] args) throws Exception {
		init();
		getRootEle();
		getChildEles();
		getPartEles();
		haveChildsEles();
		getLevelEles();
		getAttrEles();

		//打印根节点下的所有元素节点
		System.out.println(doc.getDocumentElement().getChildNodes().getLength());
		NodeList nodeList = doc.getDocumentElement().getChildNodes();
		for (int i = 0; i < nodeList.getLength(); i++) {
			if (nodeList.item(i).getNodeType() == Node.ELEMENT_NODE) {
				System.out.print(nodeList.item(i).getNodeName() + " ");
			}
		}
	}

	// 初始化Document、XPath对象
	public static void init() throws Exception {
		// 创建Document对象
		DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
		dbf.setValidating(false);
		DocumentBuilder db = dbf.newDocumentBuilder();
		doc = db.parse(new FileInputStream(new File("demo.xml")));

		// 创建XPath对象
		XPathFactory factory = XPathFactory.newInstance();
		xpath = factory.newXPath();
	}

	// 获取根元素
	// 表达式可以更换为/*,/rss
	public static void getRootEle() throws XPathExpressionException {
		Node node = (Node) xpath.evaluate("/rss", doc, XPathConstants.NODE);
		System.out.println(node.getNodeName() + "--------"
				+ node.getNodeValue());
	}

	// 获取子元素并打印
	public static void getChildEles() throws XPathExpressionException {
		NodeList nodeList = (NodeList) xpath.evaluate("/rss/channel/*", doc,
				XPathConstants.NODESET);
		for (int i = 0; i < nodeList.getLength(); i++) {
			System.out.print(nodeList.item(i).getNodeName() + " ");
		}
		System.out.println();
	}

	// 获取部分元素
	// 只获取元素名称为title的元素
	public static void getPartEles() throws XPathExpressionException {
		NodeList nodeList = (NodeList) xpath.evaluate("//*[name() = 'title']",
				doc, XPathConstants.NODESET);
		for (int i = 0; i < nodeList.getLength(); i++) {
			System.out.print(nodeList.item(i).getNodeName() + "-->"
					+ nodeList.item(i).getTextContent());
		}
		System.out.println();
	}

	// 获取包含子节点的元素
	public static void haveChildsEles() throws XPathExpressionException {
		NodeList nodeList = (NodeList) xpath.evaluate("//*[*]", doc,
				XPathConstants.NODESET);
		for (int i = 0; i < nodeList.getLength(); i++) {
			System.out.print(nodeList.item(i).getNodeName() + " ");
		}
		System.out.println();
	}

	// 获取指定层级的元素
	public static void getLevelEles() throws XPathExpressionException {
		NodeList nodeList = (NodeList) xpath.evaluate("/*/*/*/*", doc,
				XPathConstants.NODESET);
		for (int i = 0; i < nodeList.getLength(); i++) {
			System.out.print(nodeList.item(i).getNodeName() + "-->"
					+ nodeList.item(i).getTextContent() + " ");
		}
		System.out.println("-----------------------------");
	}

	// 获取指定属性的元素
	// 获取所有大于指定价格的书箱
	public static void getAttrEles() throws XPathExpressionException {
		NodeList nodeList = (NodeList) xpath.evaluate("//bookstore/book[price>35.00]/title", doc,
				XPathConstants.NODESET);
		for (int i = 0; i < nodeList.getLength(); i++) {
			System.out.print(nodeList.item(i).getNodeName() + "-->"
					+ nodeList.item(i).getTextContent() + " ");
		}
		System.out.println();
	}
}

使用的XML文档

<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0">
	<channel>
		<title>Java Tutorials and Examples 2</title>
		<language>en-us</language>
		<item>
			<title><![CDATA[Java Tutorials 2]]></title>
			<link>http://www.javacodegeeks.com/</link>
		</item>
		<item>
			<title><![CDATA[Java Examples 2]]></title>
			<link>http://examples.javacodegeeks.com/</link>
		</item>
	</channel>
	<college name="c1">
		<class name="class1">
			<student name="stu1" sex='male' age="21" />
			<student name="stu2" sex='female' age="20" />
			<student name="stu3" sex='female' age="20" />
		</class>
	</college>
	<bookstore>
		<book>
			<title lang="eng">Harry Potter</title>
			<price>29.99</price>
		</book>
		<book>
			<title lang="eng">Learning XML</title>
			<price>39.95</price>
		</book>
	</bookstore>
</rss>