java使用XPath查找xml节点

原文地址：http://outofmemory.cn/code-snippet/2778/java-usage-XPath-seek-xml-jiedian

java 代码，通过xpath 从xml文件中查找到节点，并可转换成String输出。

package cn.outofmemory.snippets.core;

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.XPathFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class FindElementsByAbsoluteLocationWithXPath {

    public static void main(String[] args) throws Exception {

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        dbf.setValidating(false);
        DocumentBuilder db = dbf.newDocumentBuilder();

        Document doc = db.parse(new FileInputStream(new File("in.xml")));

        XPathFactory factory = XPathFactory.newInstance();

        XPath xpath = factory.newXPath();

        String expression;
        Node node;
        NodeList nodeList;

        // 1. root element
        expression = "/*";
        node = (Node) xpath.evaluate(expression, doc, XPathConstants.NODE);
        System.out.println("1. " + node.getNodeName());

        // 2. root element (by name)
        expression = "/rss";
        node = (Node) xpath.evaluate(expression, doc, XPathConstants.NODE);
        System.out.println("2. " + node.getNodeName());

        // 3. element under rss
        expression = "/rss/channel";
        node = (Node) xpath.evaluate(expression, doc, XPathConstants.NODE);
        System.out.println("3. " + node.getNodeName());

        // 4. all elements under rss/channel
        expression = "/rss/channel/*";
        nodeList = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);
        System.out.print("4. ");
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + " ");
        }
        System.out.println();

        // 5. all title elements in the document
        expression = "//title";
        nodeList = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);
        System.out.print("5. ");
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + " ");
        }
        System.out.println();

        // 6. all elements in the document except title
        expression = "//*[name() != 'title']";
        nodeList = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);
        System.out.print("6. ");
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + " ");
        }
        System.out.println();

        // 7. all elements with at least one child element
        expression = "//*[*]";
        nodeList = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);
        System.out.print("7. ");
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + " ");
        }
        System.out.println();

        // 8. all level-5 elements (the root being at level 1)
        expression = "/*/*/*/*";
        nodeList = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);
        System.out.print("8. ");
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + " ");
        }
        System.out.println();

    }

}

将node 转换成String 输出

public static String NodetoString(Node node) {
		Transformer transformer = null;
		String result = null;
		if (node == null) {
			throw new IllegalArgumentException();
		}
		try {
			transformer = TransformerFactory.newInstance().newTransformer();
		} catch (Exception e) {
			throw new RuntimeException(e.getMessage());
		}
		if (transformer != null) {
			try {
				StringWriter sw = new StringWriter();
				transformer
						.transform(new DOMSource(node), new StreamResult(sw));
				return sw.toString();
			} catch (TransformerException te) {
				throw new RuntimeException(te.getMessage());
			}
		}
		return result;
	}

Input:

xml version="1.0" encoding="UTF-8"?>
 version="2.0">
    
        
        en-us
        
            
            http://www.javacodegeeks.com/
        
        
            
            http://examples.javacodegeeks.com/