java xml按id搜索元素

Question

我们可以使用dom解析器在xml文件中按id搜索元素吗，例如：

<root>
  <context id="one">
    <entity>
      <identifier>new one</identifier>
    </entity>
  </context>

  <context id="two">
    <entity>
      <identifier>second one</identifier>
    </entity>
  </context>

</root>

我想要一个id为“one”的节点，我的代码

DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
Document document = docBuilder.parse(new File("filename.xml"));

Element ele = document.getElementById("one");

返回null

还有别的办法吗

Answer 1

可以使用JDK/JRE中的javax.xml.xpathAPI通过XPath查找元素

示例

import java.io.File;
import javax.xml.parsers.*;
import javax.xml.xpath.*;
import org.w3c.dom.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
        Document document = docBuilder.parse(new File("filename.xml"));

        XPathFactory xpathFactory = XPathFactory.newInstance();
        XPath xpath = xpathFactory.newXPath();
        Element element = (Element) xpath.evaluate("//*[@id='one']", document, XPathConstants.NODE);
    }

}

Answer 2

尝试使用XML-Xpath表达式，这非常简单

File fXmlFile = new File("filePath");
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(fXmlFile);


doc.getDocumentElement().normalize();
System.out.println("Root element :" + doc.getDocumentElement().getNodeName());


XPathFactory factory = XPathFactory.newInstance();

            XPath xpath = factory.newXPath();

            String expression;
            Node node;

            // 1. elements with id '1'
            expression = "//context[@id='one']"; 
            node = (Node ) xpath.evaluate(expression, doc, XPathConstants.NODE);