Parsing XML files using Dom4j

One 、XML analysis Basic knowledge of

1.1 XML Parse type

        XML There are ways of parsing 4 Kind of , Namely ：DOM analysis 、SAX analysis 、JDOM analysis 、DOM4j analysis . The first two are basic methods , It's official It's not about the platform The latter two are extension methods , It is developed on the basis of basic methods , Only applicable to java platform .
        

1、DOM analysis ：JDK They all come with them , No need to import the package . The parser is required to convert the whole XML All files are loaded into memory , Generate a Document object .

• advantage ： Keep structure between elements 、 Relationship , You can add, delete, modify and query elements
• shortcoming ：XML File is too large. , May cause memory overflow

2、SAX analysis ： It's faster , More efficient parsing , It is progressive scanning Of , Scan and analyze , And take Event driven approach To carry out specific analysis , Each row parsed will trigger an event .

• advantage ： There will be no memory overflow problem, and you can deal with large files
• shortcoming ： Intelligent reading , Can't write

1.2 Parser

The parser is to provide specific implementation according to different parsing methods , In order to facilitate developers to parse XML, There are some convenient class libraries .

• dom4j： It's relatively simple XML Parsed class library
• Jsoup： It's powerful DOM Way to resolve the class library , Especially for HTML The parsing of is more convenient

Two 、 Use dom4j analysis XML

2.1 Set up the environment

Create a maven project

Will project's maven Change warehouse to local warehouse

Join the rely on

<!-- https://mvnrepository.com/artifact/org.dom4j/dom4j -->
<dependency>
    <groupId>org.dom4j</groupId>
    <artifactId>dom4j</artifactId>
    <version>2.1.3</version>
</dependency>

stay resources Created in the root directory user.xml file ,

And in user.xml Add the following to the file

<?xml version="1.0" encoding="UTF-8" ?>
<users>
    <user id="10001" country="Chinese" source="Android">
        <id>10001</id>
        <name>admin</name>
        <password>111111</password>
    </user>

    <user id="10002" country="Chinese" source="ios">
        <id>10002</id>
        <name>tony</name>
        <password>666666</password>
    </user>

</users>

2.2 analysis XML file

Introduction to parsing steps

1、 Create parser object

 // Create parser object 
    SAXReader saxReader = new SAXReader();

2、 Use the parser object to read XML Document generation Document object

 Document document = saxReader.read(Dom4jParseUserXmlTest.class.getClassLoader().getResource("user.xml"));

3、 according to Document Object acquisition XML The elements of ( Tag information )

            //3.1  obtain XML The root node of the file 
            Element rootElement = document.getRootElement();
            System.out.println("user.xml The name of the root node of the file is "+rootElement.getName());
            //3.2  obtain XML The child node under the root node of the file 
            System.out.println(" Get root tag users List of sub tags ");
            List<Element> usersSubElementList = rootElement.elements();
            for (Element userElement : usersSubElementList) {
    
                //String attributeValue(String name); Get the attribute value of the specified attribute name 
                System.out.println("users Child of the tag "+userElement.getName());
                System.out.println("users Sub tag of tag id The property value is "+userElement.attributeValue("id"));
                System.out.println("users Sub tag of tag country Property value "+userElement.attributeValue("country"));
                System.out.println("users Sub tag of tag sources Property value "+userElement.attributeValue("source"));
                System.out.println("3、 obtain user List of sub tags ");

Create name as Dom4jParseUserXmlTest Class , And add the following , Start parsing

package com.li.dom4j;

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

import java.util.List;

/** * @author potential */
public class Dom4jParseUserXmlTest {
    
    public static void main(String[] args)  {
    
        //1、 Create parser object 
        SAXReader saxReader = new SAXReader();
        //2、 Use the parser object to read XML Document generation Document object  try {
    
            Document document = saxReader.read(Dom4jParseUserXmlTest.class.getClassLoader().getResource("user.xml"));
            //3、 according to Document Object acquisition XML Element label information 

            /** * 1、org.dom4j.Document Common methods  * Element getRootElement();  obtain XML The root node of the file  * 2、org.dom4j.Element Common methods  * String getName(); return  * List<Element>elements(); Get the sub tag of the tag  */
            //3.1  obtain XML The root node of the file 
            Element rootElement = document.getRootElement();
            System.out.println("user.xml The name of the root node of the file is "+rootElement.getName());
            //3.2  obtain XML The child node under the root node of the file 
            System.out.println(" Get root tag users List of sub tags ");
            List<Element> usersSubElementList = rootElement.elements();
            for (Element userElement : usersSubElementList) {
    
                //String attributeValue(String name); Get the attribute value of the specified attribute name 
                System.out.println("users Child of the tag "+userElement.getName());
                System.out.println("users Sub tag of tag id The property value is "+userElement.attributeValue("id"));
                System.out.println("users Sub tag of tag country Property value "+userElement.attributeValue("country"));
                System.out.println("users Sub tag of tag sources Property value "+userElement.attributeValue("source"));
                System.out.println("3、 obtain user List of sub tags ");
                List<Element> userSubElementList = userElement.elements();
                for (Element userSubElement : userSubElementList) {
    
                    System.out.println("user The sub tag name under the tag is "+userSubElement.getName());
                    //String getText(); Get the text of the tag 
                    System.out.println("user The text of the sub tag under the tag is "+userSubElement.getText());

                }
            }
            // obtain users The first of the labels user label 
            Element firstUserElement = rootElement.element("user");
            // Get the first one user Sub tags under tags password Text for property 
            //String elementText(String name); Get the text of the sub label of the specified name 
            String password = firstUserElement.elementText("password");
            System.out.println(" first user Child of the tag password The text of "+password);
        } catch (DocumentException e) {
    
            e.printStackTrace();
        }
    }
}

Operation result display

2.3 dom4j important API explain

org.dom4j.Document Common methods

Element getRootElement()	obtain XML The root node of the file

org.dom4j.Element Common methods

String getName()	Return the element name
Listelements()	Get the sub tag of the tag
String attributeValue(String name)	Get the attribute value of the specified attribute name
String getText()	Get the text of the tag
String elementText(String name)	Get the text of the sub label of the specified name