Java8 xpath 示例 – 在字符串上求值 xpath

原文： https://howtodoinjava.com/xml/evaluate-xpath-on-xml-string/

Java 示例求值字符串上的 xpath 并返回字符串本身的结果 XML。

1. XPath 示例 – 在 xml 字符串上求值 xpath

1. 创建包含StringReader并引用 XML 字符串的org.xml.sax.InputSource。
2. 从XPathFactory创建XPath。
3. 使用xpath.evaluate('expression', inputSource)获取结果 HTML。

package com.howtodoinjava.demo;
import java.io.StringReader;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
public class XPathExample 
{
    public static void main(String[] args) throws Exception 
    {
        String xml = "<employees>"
                    + "<employee id=\"1\">"
                        + "<firstName>Lokesh</firstName>"
                        + "<lastName>Gupta</lastName>"
                        + "<department><id>101</id><name>IT</name></department>"
                    + "</employee>"
                   + "</employees>";
        InputSource inputXML = new InputSource( new StringReader( xml ) );
        XPath xPath = XPathFactory.newInstance().newXPath();
        String result = xPath.evaluate("/employees/employee/firstName", inputXML);
        System.out.println(result);
    }
}

程序输出：

Lokesh

2. XPath 示例 – 在 xml 文件上求值 xpath

package com.howtodoinjava.demo;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
public class XPathExample 
{
    public static void main(String[] args) throws Exception 
    {
        String xmlFile = "employees.xml";
        //Get DOM
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document xml = db.parse(xmlFile);
        //Get XPath 
        XPathFactory xpf = XPathFactory.newInstance();
        XPath xpath = xpf.newXPath();
        //Get first match
        String name = (String) xpath.evaluate("/employees/employee/firstName", xml, XPathConstants.STRING);
        System.out.println(name);    //Lokesh
        //Get all matches
        NodeList nodes = (NodeList) xpath.evaluate("/employees/employee/@id", xml, XPathConstants.NODESET);
        for (int i = 0; i < nodes.getLength(); i++) {
            System.out.println(nodes.item(i).getNodeValue());    //1 2
        }
    }
}

程序输出：

Lokesh
1
2

输入的 xml 文件为：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<employees>
    <employee id="1">
        <firstName>Lokesh</firstName>
        <lastName>Gupta</lastName>
        <department>
            <id>101</id>
            <name>IT</name>
        </department>
    </employee>
    <employee id="2">
        <firstName>Brian</firstName>
        <lastName>Schultz</lastName>
        <department>
            <id>102</id>
            <name>HR</name>
        </department>
    </employee>
</employees>

在上面的 Xpath 教程中，我们学习了使用示例求值字符串上的 xpath 的方法。

学习愉快！

阅读更多：

文件中的 Java xpath 示例

Java xpath 教程

如何在 Java 中使用 xpath 获取 xml 中的属性值