Java 如何使用XPath检查XML内容中是否存在节点？
Java 如何检查XML中是否存在某个属性？

要检查节点是否存在，我们可以执行 xpath 表达式并查看匹配的节点数量。

示例：

package com.onitroad.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 {
		// 从 XML 获取DOM
		String fileName = "employees.xml";
		Document document = getDocument(fileName);
		String xpathExpression = "";
		// 获取所有 employee的 firstName
		xpathExpression = "/employees/employee/firstName";
		System.out.println(checkIfNodeExists(document, xpathExpression));	//true

		// 获取所有id
		xpathExpression = "/employees/employee/@id";
		System.out.println(checkIfNodeExists(document, xpathExpression));	//true

		// 获取所有年龄
		xpathExpression = "/employees/employee/@age";
		System.out.println(checkIfNodeExists(document, xpathExpression));	//false
		
		// 获取所有部门
		xpathExpression = "/employees/employee/department/name";
		System.out.println(checkIfNodeExists(document, xpathExpression));	//true

		// 获取部门位置
		xpathExpression = "/employees/employee/department/location";
		System.out.println(checkIfNodeExists(document, xpathExpression));	//false
	}
	private static boolean checkIfNodeExists(Document document, String xpathExpression) throws Exception 
	{
		boolean matches = false;

		// 创建 XPathFactory 对象
		XPathFactory xpathFactory = XPathFactory.newInstance();
		// 创建 XPath 对象
		XPath xpath = xpathFactory.newXPath();
		try {
			// 创建 XPathExpression 对象
			XPathExpression expr = xpath.compile(xpathExpression);
			// 在XML文档上计算表达式结果
			NodeList nodes = (NodeList) expr.evaluate(document, XPathConstants.NODESET);

			if(nodes != null  && nodes.getLength() > 0) {
				matches = true;
			}
		} catch (XPathExpressionException e) {
			e.printStackTrace();
		}
		return matches;
	}

	private static Document getDocument(String fileName) throws Exception {
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		factory.setNamespaceAware(true);
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document doc = builder.parse(fileName);
		return doc;
	}	
}