XPathTechnology

is the XML path language, which is a path language used to determine XML (subset of Standard Universal Markup Language) The language of a portion of a document. XPathThe tree structure based on XML provides the ability to find nodes in the data structure tree. The original intention of XPath was to use it as a universal interface between XPointer and XSLT# Grammar model between ##. But XPath was quickly adopted by developers as a small query language.

: It cooperates with DOM4J parsing technology to make up for DOM4J The disadvantage of not being able to get elements across layers. The jaxen-1.1-beta-6.jar package needs to be introduced.

XPath

XPath

SQLQuery statement can query the DOM tree and obtain the corresponding results.

XPath

<?xml version="1.0" encoding="utf-8"?>
<AAA>
	<BBB id="b1">Hello World B1</BBB>
	<CCC id="c1"/>
	<BBB id="b2">Hello World B2</BBB>
	<BBB>Hello World B3</BBB>
	<DDD>
		<BBB id="b3">Hello World B4</BBB>
	</DDD>
	<CCC>
		<DDD>
			<BBB id="b4"/>
			<BBB id="b5"/>
		</DDD>
	</CCC>
</AAA>

package com.pc;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Iterator;
import java.util.List;

import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;

/**
 * 
 * @author Switch
 * @function DOM4j配合xpath
 * 
 */
public class XML9 {
	public static void main(String[] args) throws Exception {
		// 1.得到SAXReader解析器
		SAXReader saxReader = new SAXReader();
		// 2.指定解析哪个文件
		Document document = saxReader.read("src/com/pc/XML9.xml");
		// 3.使用XPath随意读取任何一层的元素
		// document.selectNodes(); //返回多个元素
		// document.selectSingleNode(); // 返回一个元素

		// 取出AAA下面的所有BBB 3个
		// List nodeList = document.selectNodes("/AAA/BBB");
		// 取出所有的BBB 6个
		// List nodeList = document.selectNodes("//BBB");
		// System.out.println(nodeList.size());

		// 取出AAA下面的DDD下面的最后一个BBB元素的内容 Hello World B4
		// List nodeList = document.selectNodes("/AAA/DDD//BBB[last()]");
		// System.out.println(((Element)nodeList.get(0)).getTextTrim());

		// 取出AAA下面的CCC下面的DDD下面的所有元素 2个
		// List nodeList = document.selectNodes("/AAA/CCC/DDD/*");

		// 取出所有有三个祖先元素的BBB元素
		// List nodeList = document.selectNodes("/*/*/*/BBB");
		// System.out.println(nodeList.size());

		// 取出AAA下面的第一个BBB元素的内容 Hello World B1
		// List nodeList = document.selectNodes("/AAA/BBB[1]");
		// System.out.println(((Element)nodeList.get(0)).getTextTrim());
		// Element element = (Element) document.selectSingleNode("/AAA/BBB[1]");
		// System.out.println(element.getTextTrim());

		// 取出所有有id属性的元素的id属性 5个
		// List nodeList = document.selectNodes("//@id");
		// System.out.println(nodeList.size());
		// 取出第一个有id属性的元素的id属性的值 b1
		// System.out.println(((Attribute)nodeList.get(0)).getText());

		// 取出所有有id属性的CCC元素
		// List nodeList = document.selectNodes("//CCC[@id]");
		// System.out.println(nodeList.size());

		// "//BBB[@*]" 选择有任意属性的BBB元素

		// "//BBB[not(@*)]" 选择没有属性的BBB元素

		// "//BBB[@id='b1']" 选择含有属性id且其值为'b1'的BBB元素

		// 选择含有属性id且其值(在用normalize-space函数去掉前后空格后)为'b2'的BBB元素
		// "//BBB[normalize-space(@id)='b2']"

		// "//*[count(BBB)=2]" 选择含有2个BBB子元素的元素

		// "//*[name()='BBB']" 选择所有名称为BBB的元素(这里等价于//BBB)

		// "//*[starts-with(name(),'B')]" 选择所有名称以"B"起始的元素

		// "//*[contains(name(),'C')]" 选择所有名称包含"C"的元素

		// "//*[string-length(name()) = 3]" 选择名字长度为3的元素

		// "//*[string-length(name()) < 4]" 选择名字长度小于3的元素
		// 同样的将<替换成大于号则是大于
		// 11个
		// List nodeList = document.selectNodes("//*[string-length(name()) < 4]");
		// System.out.println(nodeList.size());
		
		// "//CCC | //BBB" 选择所有的CCC和BBB元素
	}
}

: Through the XPath statement in the above case, the basic XML query, there is no problem in using it.

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