XMLPath的基本使用

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什么是XPath

XPath是一种用于在xml格式的内容中提取信息的方式. 它与从JSON中提取信息的JSONPath类似. (如何使用JSONPath). 本文将介绍xpath的基本格式以及在Java中如何使用Xpath提取信息.

XPath基本格式

XPath的表达式

一般表达式格式如下: /foo/bar 可以搜索如下的xml内容/节点:

<foo>
     <bar/>
foo>
或者:
<foo>
     <bar/>
     <bar/>
     <bar/>
foo>

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如果以// 开始代表忽略深度限制.

常见的节点元素类型:

预测允许我们来查找满足条件的节点. 格式是[表达式]. 比如:

选择所有foo节点(含所有子节点,孙子节点...)包含include属性,且值为true
//foo[@include='true']

//foo[@include='true'][@mode='bar']
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更多的预测格式

<Tutorials>
    <Tutorial tutId="01" type="java">
        <title>Guavatitle>
        <description>Introduction to Guavadescription>
        <date>04/04/2016date>
        <author>GuavaAuthorauthor>
    Tutorial>
    <Tutorial tutId="02" type="java">
        <title>XMLtitle>
        <description>Introduction to XPathdescription>
        <date>04/05/2016date>
        <author>XMLAuthorauthor>
    Tutorial>
Tutorials>
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比如上面的例子:

/Tutorials/Tutorial[1]

/Tutorials/Tutorial[first()]

/Tutorials/Tutorial[position()<4]
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XPath在Java中的使用示例

JDK11中原生支持了xmlpath解析, 以解析上面的xml为例:

获取一堆节点

返回所有 /Tutorials/Tutorial 节点:

import org.w3c.dom.*;

import javax.xml.parsers.*;
import javax.xml.xpath.*;
import java.io.*;

public class XmlDemo {
    public static void main(String[] args) throws Exception {
        DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = builderFactory.newDocumentBuilder();
        Document xmlDocument = builder.parse(new ByteArrayInputStream(EXAMPLE_STRING.getBytes()));
        XPath xPath = XPathFactory.newInstance().newXPath();
        String expression = "/Tutorials/Tutorial";
        NodeList nodeList = (NodeList) xPath.compile(expression).evaluate(xmlDocument, XPathConstants.NODESET);
        System.out.println("Find nodes length = " + nodeList.getLength());
    }




    static String EXAMPLE_STRING = "" +
            "\n" +
            "    \n" +
            "        \n" +
            "  Introduction to Guava\n" +
            "  04/04/2016\n" +
            "  GuavaAuthor\n" +
            "    \n" +
            "    \n" +
            "        \n" +
            "  Introduction to XPath\n" +
            "  04/05/2016\n" +
            "  XMLAuthor\n" +
            "    \n" +
            "";
}

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根据某个id获取节点:

获取Tutorial (tutId=01)的节点:

        String expression = "/Tutorials/Tutorial[@tutId=\"01\"]";
        Node node = (Node) xPath.compile(expression).evaluate(xmlDocument, XPathConstants.NODE);
        System.out.println("Find node" + node);
    


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根据某个tag获取节点:

获取包含title的节点 以及节点值为Guava:

        String expression = "//Tutorial[descendant::title[text()=" + "'" + "Guava" + "'" + "]]";
        NodeList nodeList = (NodeList) xPath.compile(expression).evaluate(xmlDocument, XPathConstants.NODESET);
        System.out.println("Found title=Guava length:" + nodeList.getLength());
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参考

1.JDK中的api

2.在线测试xmlpath