Query XML documents with XPath

One 、XPath Path expression

XPath The path expression is XML The language in which data is queried in the document

expression	describe
nodename	Select all children of this node
/	Select from root node
//	Select the node of the document from the current node that matches the selection , Regardless of its location
.	Select the current node
…	Select the parent of the current node
@	Select Properties

Two 、jaxen

Jaxen It's a Java Compiling XPath library , It can adapt to many different object models , Such as ：DOM,XOM,dom4j etc. .

Dom4j The underlying dependence Jaxen Realization Xpath Inquire about

3、 ... and 、 Program realization

xml page

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hr SYSTEM "hr.dtd"><!--  Human resource management system  -->
<hr>
	<employee no="3301">
		<name> Zhang San </name>
		<age>31</age>
		<salary>3500</salary>
		<department>
			<dname> The administration department </dname>
			<address>xx building -B103</address>
		</department>
	</employee>
	
	<employee no="3302">
		<name> Zhang Si </name>
		<age>32</age>
		<salary>4500</salary>
		<department>
			<dname> The administration department </dname>
			<address>xx building -B103</address>
		</department>
	</employee>
	
	<employee no="3303">
		<name> Zhang Wu </name>
		<age>33</age>
		<salary>5200</salary>
		<department>
			<dname> The administration department </dname>
			<address>xx building -B103</address>
		</department>
	</employee>
	
	<employee no="3304">
		<name> Zhang Liu </name>
		<age>34</age>
		<salary>5500</salary>
		<department>
			<dname> The administration department </dname>
			<address>xx building -B103</address>
		</department>
	</employee>

	<employee no="3305">
		<name> Li Si </name>
		<age>29</age>
		<salary>8000</salary>
		<department>
			<dname> Technology Department </dname>
			<address>xx building -B104</address>
		</department>
	</employee>
	
	<employee no="3306">
		<name> Li Wu </name>
		<age>26</age>
		<salary>7000</salary>
		<department>
			<dname> Technology Department </dname>
			<address>xx building -B104</address>
		</department>
	</employee>

	<employee no="3307">
		<name> Wang Wu </name>
		<age>24</age>
		<salary>3600</salary>
		<department>
			<dname> The personnel department </dname>
			<address>XX building -B205</address>
		</department>
	</employee>
</hr>

java page

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=' Li Si ']");
// tester.xpath("//employee[@no=3305]");
// tester.xpath("//employee[1]");
// tester.xpath("//employee[last()]");
// tester.xpath("//employee[position()<4]");
		tester.xpath("//employee[3] | //employee[5]");
	}
}

Four 、 Query output

1. Overall query
   tester.xpath("//employee");
   

2. Wages less than 4000 The employees'
   tester.xpath("//employee[salary<4000]");
   

3. lookup " Li Si " This employee
   tester.xpath("//employee[name=' Li Si ']");
   

4. The number is “3305” The employees'
   tester.xpath("//employee[@no=3305]");
   

5. The first employee
   tester.xpath("//employee[1]");

6. The last employee
   tester.xpath("//employee[last()]");
   

7. The first three employees
   tester.xpath("//employee[position()<4]");
   

8. The third and fifth employees
   tester.xpath("//employee[3] | //employee[5]");