使用XPath对象解析xml文件

使用XPath对象解析xml文件

1.DocumentBuilderFactory类  工厂API，使应用程序能从XML文档获取生成DOM对象树的解析器

其构造方法受保护，用newInstance()实例化

2.创建解析器

DocumentBuilder

使用这个类，应用程序员可以从XML获得一个Document。

 这个类的实例可从DocumentBuilderFactory.newDocumentBuilder()方法获得。

一旦获得此类实例，可以从各种输入源解析XML。这些输入源是InputStreams,Files,URL和SAX InputSources。

----其构造方法是受保护的

public static void main(String[] args) throws Exception {
        // 创建解析工厂
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        // 创建解析器
        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
        // 通过解析器读取配置文件--返回Document对象树--org.w3c.dom.Document
        Document doc = documentBuilder.parse("config/bookstore.xml");

        // 创建XPath对象
        XPathFactory xPathFactory = XPathFactory.newInstance();
        XPath xPath = xPathFactory.newXPath();
        /*
         * 1.获取bookstore节点下的book属性category值为web下的第二个 title节点的文本内容
         * bookstore-》book[@category='web'][2]-》title
         * xpath路径：/bookstore/book[@category='web'][2]/title/text()
         */
        String titleXpath = "/bookstore/book[@category='web'][2]/title/text()";
        String titleVlue = (String) xPath.evaluate(titleXpath, doc, XPathConstants.STRING);
        System.out.println("1:" + titleVlue);
        /*
         * 2.获取bookstore节点下book属性category值为web的title属性为en的节点内容
         * xpath路径：/bookstore/book[@category='web']/title[@lang='en']/text() 选取属性为en
         * 的title[@lang='en']
         */
        String titleXpath2 = "/bookstore/book[@category='web']/title[@lang='en']/text()";
        String titleValue2 = (String) xPath.evaluate(titleXpath2, doc, XPathConstants.STRING);
        System.out.println("2:" + titleValue2);
        /*
         * 3.获取bookstore下book属性category值为cooking的title的lang属性的值
         * xpath路径：/bookstore/book[@category='cooking']/title/@lang
         */
        // 获取属性的值
        String str1 = "/bookstore/book[@category='cooking']/title/@lang";
        String shuxing = (String) xPath.evaluate(str1, doc, XPathConstants.STRING);
        System.out.println("3:" + shuxing);
        /*
         * 4.获取bookstore节点下的所有book的节点集合 /bookstore/book
         */
        // 返回值是节点集合
        String str3 = "/bookstore/book";
        NodeList all = (NodeList) xPath.evaluate(str3, doc, XPathConstants.NODESET);
        // 开始遍历集合
        for (int i = 0; i < all.getLength(); i++) {
            // book节点
            Element bookelt = (Element) all.item(i);// i是获取第几个
            String titleValue = (String) xPath.evaluate("title", bookelt, XPathConstants.STRING);
            String authorValue = (String) xPath.evaluate("author", bookelt, XPathConstants.STRING);
            String yearValue = (String) xPath.evaluate("year", bookelt, XPathConstants.STRING);
            String priceValue = (String) xPath.evaluate("price", bookelt, XPathConstants.STRING);

            System.out.println(
                    "title:" + titleValue + " author:" + authorValue + " year:" + yearValue + " price:" + priceValue);

        }
    }

//config/bookstore.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
1.获取bookstore节点下的book属性category值为web下的第二个
title节点的文本内容
bookstore-》book[@category='web'][2]-》title
xpath路径：/bookstore/book[@category='web'][2]/title/text()
 -->
 <!-- 
 2.获取bookstore节点下book属性category值为web的title属性为en的节点内容
 xpath路径：/bookstore/book[@category='web']/title[@lang='en']
 选取属性为en 的title[@lang='en']
  -->
 <!-- 
 3.获取bookstore下book属性category值为cooking的title的lang属性的值
 xpath路径：/bookstore/book[@category='cooking']/title/@lang
  -->
 <!-- 
 4.获取bookstore节点下的所有book的节点集合
 /bookstore/book
  -->
<bookstore>
    <book category="children">
        <title lang="en">Harry Potter</title>
        <author>J K. Rowling</author>
        <year>2005</year>
        <price>29.99</price>
    </book>
    <book category="cooking">
        <title lang="en">Everyday Italian</title>
        <author>Giada De Laurentiis</author>
        <year>2005</year>
        <price>30.00</price>
    </book>
    <book category="web">
        <title lang="en">Learning XML</title>
        <author>XJS</author>
        <year>2019</year>
        <price>79.88</price>
    </book>
    <book category="web">
        <title lang="uk">Learning stack</title>
        <author>XJS</author>
        <year>2019</year>
        <price>100.00</price>
    </book>
</bookstore>