XMLPath的基本使用

[aviation]

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>

如果以// 开始代表忽略深度限制.

常见的节点元素类型:

Location Path	Description
/foo/bar/@id	bar元素的id属性
/foo/bar/text()	bar元素的text值.

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']

更多的预测格式

<?xml version="1.0"?>
<Tutorials>
    <Tutorial tutId="01" type="java">
        <title>Guava</title>
        <description>Introduction to Guava</description>
        <date>04/04/2016</date>
        <author>GuavaAuthor</author>
    </Tutorial>
    <Tutorial tutId="02" type="java">
        <title>XML</title>
        <description>Introduction to XPath</description>
        <date>04/05/2016</date>
        <author>XMLAuthor</author>
    </Tutorial>
</Tutorials>

比如上面的例子:

/Tutorials/Tutorial[1]

/Tutorials/Tutorial[first()]

/Tutorials/Tutorial[position()<4]

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 = "<?xml version=\"1.0\"?>" +
            "<Tutorials>\n" +
            "    <Tutorial tutId=\"01\" type=\"java\">\n" +
            "        <title>Guava</title>\n" +
            "  <description>Introduction to Guava</description>\n" +
            "  <date>04/04/2016</date>\n" +
            "  <author>GuavaAuthor</author>\n" +
            "    </Tutorial>\n" +
            "    <Tutorial tutId=\"02\" type=\"java\">\n" +
            "        <title>XML</title>\n" +
            "  <description>Introduction to XPath</description>\n" +
            "  <date>04/05/2016</date>\n" +
            "  <author>XMLAuthor</author>\n" +
            "    </Tutorial>\n" +
            "</Tutorials>";
}

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);
    

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());

参考

1.JDK中的api

2.在线测试xmlpath