XPath实现XML文档的查询

一、XPath路径表达式

XPath路径表达式是XML文档中查询数据的语言

表达式	描述
nodename	选取此节点的所有子节点
/	从根节点选取
//	从匹配选择的当前节点选择文档的节点，不考虑其位置
.	选取当前节点
…	选取当前节点的父节点
@	选取属性

二、jaxen

Jaxen是一个Java编写的XPath库，可以适应多种不同的对象模型，如：DOM，XOM，dom4j等。

Dom4j底层依赖Jaxen实现Xpath查询

三、程序实现

xml页面

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hr SYSTEM "hr.dtd"><!-- 人力资源管理系统 -->
<hr>
	<employee no="3301">
		<name>张三</name>
		<age>31</age>
		<salary>3500</salary>
		<department>
			<dname>行政部</dname>
			<address>xx大厦-B103</address>
		</department>
	</employee>
	
	<employee no="3302">
		<name>张四</name>
		<age>32</age>
		<salary>4500</salary>
		<department>
			<dname>行政部</dname>
			<address>xx大厦-B103</address>
		</department>
	</employee>
	
	<employee no="3303">
		<name>张五</name>
		<age>33</age>
		<salary>5200</salary>
		<department>
			<dname>行政部</dname>
			<address>xx大厦-B103</address>
		</department>
	</employee>
	
	<employee no="3304">
		<name>张六</name>
		<age>34</age>
		<salary>5500</salary>
		<department>
			<dname>行政部</dname>
			<address>xx大厦-B103</address>
		</department>
	</employee>

	<employee no="3305">
		<name>李四</name>
		<age>29</age>
		<salary>8000</salary>
		<department>
			<dname>技术部</dname>
			<address>xx大厦-B104</address>
		</department>
	</employee>
	
	<employee no="3306">
		<name>李五</name>
		<age>26</age>
		<salary>7000</salary>
		<department>
			<dname>技术部</dname>
			<address>xx大厦-B104</address>
		</department>
	</employee>

	<employee no="3307">
		<name>王五</name>
		<age>24</age>
		<salary>3600</salary>
		<department>
			<dname>人事部</dname>
			<address>XX大厦-B205</address>
		</department>
	</employee>
</hr>

java页面

package com.imooc.dom4j;

import java.util.List;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.Node;
import org.dom4j.io.SAXReader;

public class XPathTester {
    
	public void xpath(String xpathExp) {
    
		String file = "d:/workplace/xml/src/hr.xml";
		SAXReader reader = new SAXReader();
		try {
    
			Document document = reader.read(file);
			List<Node> nodes = document.selectNodes(xpathExp);
			for(Node node :nodes) {
    
				Element emp = (Element)node;
				System.out.println(emp.attributeValue("no"));
				System.out.println(emp.elementText("name"));
				System.out.println(emp.elementText("age"));
				System.out.println(emp.elementText("salary"));
				System.out.println("=========================");
			}
		} catch (DocumentException e) {
    
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args) {
    
		XPathTester tester = new XPathTester();
// tester.xpath("/hr/employee");
// tester.xpath("//employee");
// tester.xpath("//employee[salary<4000]");
// tester.xpath("//employee[name='李四']");
// tester.xpath("//employee[@no=3305]");
// tester.xpath("//employee[1]");
// tester.xpath("//employee[last()]");
// tester.xpath("//employee[position()<4]");
		tester.xpath("//employee[3] | //employee[5]");
	}
}

四、查询输出

1. 总体查询
   tester.xpath("//employee");
   

2. 工资小于4000的员工
   tester.xpath("//employee[salary<4000]");
   

3. 查找"李四"这个员工
   tester.xpath("//employee[name='李四']");
   

4. 编号为“3305”的员工
   tester.xpath("//employee[@no=3305]");
   

5. 第一个员工
   tester.xpath("//employee[1]");

6. 最后一个员工
   tester.xpath("//employee[last()]");
   

7. 前三个员工
   tester.xpath("//employee[position()<4]");
   

8. 第三个和第五个员工
   tester.xpath("//employee[3] | //employee[5]");