XPath的使用

   前面介绍了Jsoup，现在记录一下XPath

   XPath主要是NodeSet和Node，NodeSet是节点的集合，Node是一个节点。其他的是一样的操作。

  

    XPath的操作：

 

    

package SWPU;

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.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
 
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
 
public class XPathDemo {
    private static Document doc;
    private static XPath xpath;
 
    public static void main(String[] args) throws Exception {
        init();
        getRootEle();
        getChildEles();
        getPartEles();
        haveChildsEles();
        getLevelEles();
        getAttrEles();
         
        //打印根节点下的所有元素节点
        System.out.println(doc.getDocumentElement().getChildNodes().getLength());
        NodeList nodeList = doc.getDocumentElement().getChildNodes();
        for (int i = 0; i < nodeList.getLength(); i++) {
            if (nodeList.item(i).getNodeType() == Node.ELEMENT_NODE) {
                System.out.print(nodeList.item(i).getNodeName() + " ");
            }
        }
    }
 
    // 初始化Document、XPath对象
    public static void init() throws Exception {
        // 创建Document对象
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        dbf.setValidating(false);
        DocumentBuilder db = dbf.newDocumentBuilder();
        doc = db.parse(new FileInputStream(new File("F://demo.xml")));
 
        // 创建XPath对象
        XPathFactory factory = XPathFactory.newInstance();
        xpath = factory.newXPath();
    }
 
    // 获取根元素
    // 表达式可以更换为/*,/rss
    public static void getRootEle() throws XPathExpressionException {
        Node node = (Node) xpath.evaluate("/rss", doc, XPathConstants.NODE);  //提取出相应的路径中的内容,NODE是指一个
        System.out.println(node.getNodeName() + "--------"  //getNodeName()获取节点名称
                + node.getNodeValue()); //getNodeValue()获取节点的值
    }
 
    // 获取子元素并打印
    public static void getChildEles() throws XPathExpressionException {
        NodeList nodeList = (NodeList) xpath.evaluate("/rss/channel/*", doc,  //获取的是整个元素
                XPathConstants.NODESET);     //返回的是节点列表 ，NODESET是节点列表
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + "："+nodeList.item(i).getTextContent()+"\n");//通过item()来获得每一个列表项  
        }
        System.out.println();
    }
 
    // 获取部分元素
    // 只获取元素名称为title的元素
    public static void getPartEles() throws XPathExpressionException {
        NodeList nodeList = (NodeList) xpath.evaluate("//*[name() = 'title']",
                doc, XPathConstants.NODESET);
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + "-->" 
                    + nodeList.item(i).getTextContent());
        }
        System.out.println();
    }
 
    // 获取包含子节点的元素
    public static void haveChildsEles() throws XPathExpressionException {
        NodeList nodeList = (NodeList) xpath.evaluate("//*[*]", doc,
                XPathConstants.NODESET);
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + " ");
        }
        System.out.println();
    }
 
    // 获取指定层级的元素
    public static void getLevelEles() throws XPathExpressionException {
        NodeList nodeList = (NodeList) xpath.evaluate("/*/*/*/*", doc,  //四层路径下面匹配
                XPathConstants.NODESET);
        System.out.println("LEVEL:\n");
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + "-->"
                    + nodeList.item(i).getTextContent() + "\n ");
        }
        System.out.println("-----------------------------");
    }
 
    // 获取指定属性的元素
    // 获取所有大于指定价格的书箱
    public static void getAttrEles() throws XPathExpressionException {
        NodeList nodeList = (NodeList) xpath.evaluate("//bookstore/book[price>35.00]/title", doc,
                XPathConstants.NODESET);                        //上面找的是title元素，price〉35.00作为查询条件
        System.out.println("Attibute:\n");
        for (int i = 0; i < nodeList.getLength(); i++) {
            System.out.print(nodeList.item(i).getNodeName() + "-->"
                    + nodeList.item(i).getTextContent() + " ");
        }
        System.out.println();
    }
}