一、基本概念介紹

XPath 是一門在 XML 文件中查詢資訊的語言， 可用來在 XML 文件中對元素和屬性進行遍歷。XPath 是 W3C XSLT 標準的主要元素，並且 XQuery 和 XPointer 同時被構建於 XPath 表達之上。因此，對 XPath 的理解是很多高階 XML 應用的基礎。
XPath非常類似對資料庫操作的SQL語言，或者說JQuery，它可以方便開發者抓起文件中需要的東西。（dom4j也支援xpath

1.節點型別

XPath中有七種結點型別：元素、屬性、文字、名稱空間、處理指令、註釋以及文件節點（或稱為根節點）。文件中存在元素節點，屬性節點，根節點

2.常用路徑表示式

示例如下：

3.限定語

用來查詢某個特定的節點或者包含某個指定的值的節點。以方括號括起

4.萬用字元

二、程式碼示例

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();
         
        //列印根節點下的所有元素節點
        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物件
    public static void init() throws Exception {
        // 建立Document物件
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        dbf.setValidating(false);
        DocumentBuilder db = dbf.newDocumentBuilder();
        doc = db.parse(new FileInputStream(new File("demo.xml")));
 
        // 建立XPath物件
        XPathFactory factory = XPathFactory.newInstance();
        xpath = factory.newXPath();
    }
 
    // 獲取根元素
    // 表示式可以更換為/*,/rss
    public static void getRootEle() throws XPathExpressionException {
        Node node = (Node) xpath.evaluate("/rss", doc, XPathConstants.NODE);
        System.out.println(node.getNodeName() + "--------"
                + node.getNodeValue());
    }
 
    // 獲取子元素並列印
    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();
    }
 
    // 獲取部分元素
    // 只獲取元素名稱為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();
    }
 
    // 獲取包含子節點的元素
    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();
    }
 
    // 獲取指定層級的元素
    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("-----------------------------");
    }
 
    // 獲取指定屬性的元素
    // 獲取所有大於指定價格的書箱
    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文件

<?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>

轉載：

https://www.cnblogs.com/create-and-orange/p/10948738.html

http://www.w3school.com.cn/xpath/index.asp