Java8 xpath 示例 – 在字符串上求值 xpath · HowToDoInJava 中文系列教程

# Java8 xpath 示例 – 在字符串上求值 xpath > 原文： [https://howtodoinjava.com/xml/evaluate-xpath-on-xml-string/](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結果 XML。 ## 1\. XPath 示例 – 在 xml 字符串上求值 xpath 1. 創建包含[`StringReader`](https://docs.oracle.com/javase/8/docs/api/java/io/StringReader.html)并引用 XML 字符串的[`org.xml.sax.InputSource`](https://docs.oracle.com/javase/7/docs/api/org/xml/sax/InputSource.html)。 2. 從[`XPathFactory`](https://docs.oracle.com/javase/8/docs/api/javax/xml/xpath/XPathFactory.html)創建[`XPath`](https://docs.oracle.com/javase/8/docs/api/javax/xml/xpath/XPath.html)。 3. 使用[`xpath.evaluate('expression', inputSource)`](https://docs.oracle.com/javase/8/docs/api/javax/xml/xpath/XPath.html#evaluate-java.lang.String-org.xml.sax.InputSource-)獲取結果 HTML。 ```java 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); } } ``` 程序輸出： ```java Lokesh ``` ## 2\. XPath 示例 – 在 xml 文件上求值 xpath ```java 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 } } } ``` 程序輸出： ```java Lokesh 1 2 ``` 輸入的 xml 文件為： ```java <?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，我們學習了使用示例求值字符串上的 xpath 的方法。學習愉快！閱讀更多： [文件中的 Java xpath 示例](https://howtodoinjava.com/xml/evaluate-xpath-on-dom/) [Java xpath 教程](https://howtodoinjava.com/xml/how-to-work-with-xpaths-in-java-with-examples/) [如何在 Java 中使用 xpath 獲取 xml 中的屬性值](https://howtodoinjava.com/xml/xpath-attribute-evaluate/)