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Java JDOM2 – XML 读取示例

Java JDOM2 – XML 读取示例

原文： https://howtodoinjava.com/xml/jdom2-read-parse-xml-examples/

JDOM 解析器可用于在更新 XML 内容后用于读取 XML，解析 XML 和写入 XML 文件。 它将 JDOM2 文档存储在内存中，以读取和修改其值。

将 XML 文档加载到内存中后，JDOM2 维护严格的父子类型关系。 父类型的 JDOM 实例（父）具有访问其内容的方法，子类型的 JDOM 实例（内容）具有访问其父对象的方法。

Table of Contents

Project Structure
JDOM2 Maven Dependency
Create JDOM2 Document
Read and filter XML content
Read XML Content with XPath
Complete Example
源码下载

项目结构

请创建此文件夹结构以执行示例。 这是在 Eclipse 中创建的简单 Maven 项目。

JDOM2 XML Parser

项目结构

请注意，我已经使用了 lambda 表达式和方法引用，因此您需要配置为使用 JDK 1.8。

JDOM2 Maven 依赖关系

<dependency>
	<groupId>org.jdom</groupId>
	<artifactId>jdom2</artifactId>
	<version>2.0.6</version>
</dependency>

要执行 XPath，您还需要 jaxen。

<dependency>
	<groupId>jaxen</groupId>
	<artifactId>jaxen</artifactId>
	<version>1.1.6</version>
</dependency>

创建 JDOM2 文档

您可以使用下面列出的任何解析器创建org.jdom2.Document实例。 它们都解析 XML 并返回内存中的 JDOM 文档。

  1. 使用 DOM 解析器

    private static Document getDOMParsedDocument(final String fileName) 
{
	Document document = null;
	try 
	{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		//If want to make namespace aware.
        //factory.setNamespaceAware(true);
		DocumentBuilder documentBuilder = factory.newDocumentBuilder();
		org.w3c.dom.Document w3cDocument = documentBuilder.parse(fileName);
		document = new DOMBuilder().build(w3cDocument);
	} 
	catch (IOException | SAXException | ParserConfigurationException e) 
	{
		e.printStackTrace();
	}
	return document;
}

  2. 使用 SAX 解析器

    private static Document getSAXParsedDocument(final String fileName) 
{
	SAXBuilder builder = new SAXBuilder(); 
	Document document = null;
	try 
	{
		document = builder.build(fileName);
	} 
	catch (JDOMException | IOException e) 
	{
		e.printStackTrace();
	}
	return document;
}

  3. 使用 StAX 解析器

    private static Document getStAXParsedDocument(final String fileName) 
{

	Document document = null;
	try 
	{
		XMLInputFactory factory = XMLInputFactory.newFactory();
		XMLEventReader reader = factory.createXMLEventReader(new FileReader(fileName));
		StAXEventBuilder builder = new StAXEventBuilder(); 
		document = builder.build(reader);
	} 
	catch (JDOMException | IOException | XMLStreamException e) 
	{
		e.printStackTrace();
	}
	return document;
}

读取和过滤 XML 内容

我将读取employees.xml文件。

<employees>
	<employee id="101">
		<firstName>Lokesh</firstName>
		<lastName>Gupta</lastName>
		<country>India</country>
		<department id="25">
			<name>ITS</name>
		</department>
	</employee>
	<employee id="102">
		<firstName>Brian</firstName>
		<lastName>Schultz</lastName>
		<country>USA</country>
		<department id="26">
			<name>DEV</name>
		</department>
	</employee>
</employees>

读取根节点

使用document.getRootElement()方法。

public static void main(String[] args) 
{
	String xmlFile = "employees.xml";
	Document document = getSAXParsedDocument(xmlFile);

	Element rootNode = document.getRootElement();
	System.out.println("Root Element :: " + rootNode.getName());
}

输出：

Root Element :: employees

读取属性值

使用Element.getAttributeValue()方法。

public static void main(String[] args) 
{
	String xmlFile = "employees.xml";
	Document document = getSAXParsedDocument(xmlFile);

	Element rootNode = document.getRootElement();

	rootNode.getChildren("employee").forEach( ReadXMLDemo::readEmployeeNode );
}

private static void readEmployeeNode(Element employeeNode) 
{
	//Employee Id
	System.out.println("Id : " + employeeNode.getAttributeValue("id"));
}

输出：

Id : 101
Id : 102

读取元素值

使用Element.getChildText()或Element.getText()方法。

public static void main(String[] args) 
{
	String xmlFile = "employees.xml";
	Document document = getSAXParsedDocument(xmlFile);

	Element rootNode = document.getRootElement();

	rootNode.getChildren("employee").forEach( ReadXMLDemo::readEmployeeNode );
}

private static void readEmployeeNode(Element employeeNode) 
{
	//Employee Id
	System.out.println("Id : " + employeeNode.getAttributeValue("id"));

	//First Name
	System.out.println("FirstName : " + employeeNode.getChildText("firstName"));

	//Last Name
	System.out.println("LastName : " + employeeNode.getChildText("lastName"));

	//Country
	System.out.println("country : " + employeeNode.getChild("country").getText());

	/**Read Department Content*/
	employeeNode.getChildren("department").forEach( ReadXMLDemo::readDepartmentNode );
}

private static void readDepartmentNode(Element deptNode) 
{
	//Department Id
	System.out.println("Department Id : " + deptNode.getAttributeValue("id"));

	//Department Name
	System.out.println("Department Name : " + deptNode.getChildText("name"));
}

Output:

FirstName : Lokesh
LastName : Gupta
country : India
Department Id : 25
Department Name : ITS

FirstName : Brian
LastName : Schultz
country : USA
Department Id : 26
Department Name : DEV

使用 XPath 读取 XML 内容

要使用 xpath 读取任何元素的值集，您需要编译XPathExpression并使用其evaluate()方法。

String xmlFile = "employees.xml";
Document document = getSAXParsedDocument(xmlFile);

XPathFactory xpfac = XPathFactory.instance();

//Read employee ids
XPathExpression<Attribute> xPathA = xpfac.compile("//employees/employee/@id", Filters.attribute());

for (Attribute att : xPathA.evaluate(document)) 
{
	System.out.println("Employee Ids :: " + att.getValue());
}

//Read employee first names
XPathExpression<Element> xPathN = xpfac.compile("//employees/employee/firstName", Filters.element());

for (Element element : xPathN.evaluate(document)) 
{
	System.out.println("Employee First Name :: " + element.getValue());
}

输出：

Employee Ids :: 101
Employee Ids :: 102

Employee First Name :: Lokesh
Employee First Name :: Brian

完整的 JDOM2 XML 读取示例

这是在 Java 中使用 JDOM2 读取 xml 的完整代码。

package com.howtodoinjava.demo.jdom2;

import java.io.FileReader;
import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamException;

import org.jdom2.Attribute;
import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.JDOMException;
import org.jdom2.filter.Filters;
import org.jdom2.input.DOMBuilder;
import org.jdom2.input.SAXBuilder;
import org.jdom2.input.StAXEventBuilder;
import org.jdom2.xpath.XPathExpression;
import org.jdom2.xpath.XPathFactory;
import org.xml.sax.SAXException;

@SuppressWarnings("unused")
public class ReadXMLDemo 
{	
	public static void main(String[] args) 
	{
		String xmlFile = "employees.xml";
		Document document = getSAXParsedDocument(xmlFile);

		/**Read Document Content*/

		Element rootNode = document.getRootElement();
		System.out.println("Root Element :: " + rootNode.getName());

		System.out.println("\n=================================\n");

		/**Read Employee Content*/

		rootNode.getChildren("employee").forEach( ReadXMLDemo::readEmployeeNode );

		System.out.println("\n=================================\n");

		readByXPath(document);
	}

	private static void readEmployeeNode(Element employeeNode) 
	{
		//Employee Id
		System.out.println("Id : " + employeeNode.getAttributeValue("id"));

		//First Name
		System.out.println("FirstName : " + employeeNode.getChildText("firstName"));

		//Last Name
		System.out.println("LastName : " + employeeNode.getChildText("lastName"));

		//Country
		System.out.println("country : " + employeeNode.getChild("country").getText());

		/**Read Department Content*/
		employeeNode.getChildren("department").forEach( ReadXMLDemo::readDepartmentNode );
	}

	private static void readDepartmentNode(Element deptNode) 
	{
		//Department Id
		System.out.println("Department Id : " + deptNode.getAttributeValue("id"));

		//Department Name
		System.out.println("Department Name : " + deptNode.getChildText("name"));
	}

	private static void readByXPath(Document document) 
	{
		//Read employee ids
		XPathFactory xpfac = XPathFactory.instance();
		XPathExpression<Attribute> xPathA = xpfac.compile("//employees/employee/@id", Filters.attribute());
		for (Attribute att : xPathA.evaluate(document)) 
		{
			System.out.println("Employee Ids :: " + att.getValue());
		}

		XPathExpression<Element> xPathN = xpfac.compile("//employees/employee/firstName", Filters.element());
		for (Element element : xPathN.evaluate(document)) 
		{
			System.out.println("Employee First Name :: " + element.getValue());
		}
	}

	private static Document getSAXParsedDocument(final String fileName) 
	{
		SAXBuilder builder = new SAXBuilder(); 
		Document document = null;
		try 
		{
			document = builder.build(fileName);
		} 
		catch (JDOMException | IOException e) 
		{
			e.printStackTrace();
		}
		return document;
	}

	private static Document getStAXParsedDocument(final String fileName) 
	{

		Document document = null;
		try 
		{
			XMLInputFactory factory = XMLInputFactory.newFactory();
			XMLEventReader reader = factory.createXMLEventReader(new FileReader(fileName));
			StAXEventBuilder builder = new StAXEventBuilder(); 
			document = builder.build(reader);
		} 
		catch (JDOMException | IOException | XMLStreamException e) 
		{
			e.printStackTrace();
		}
		return document;
	}

	private static Document getDOMParsedDocument(final String fileName) 
	{
		Document document = null;
		try 
		{
			DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
			//If want to make namespace aware.
	        //factory.setNamespaceAware(true);
			DocumentBuilder documentBuilder = factory.newDocumentBuilder();
			org.w3c.dom.Document w3cDocument = documentBuilder.parse(fileName);
			document = new DOMBuilder().build(w3cDocument);
		} 
		catch (IOException | SAXException | ParserConfigurationException e) 
		{
			e.printStackTrace();
		}
		return document;
	}

	/*private static String readFileContent(String filePath) 
	{
	    StringBuilder contentBuilder = new StringBuilder();
	    try (Stream<String> stream = Files.lines( Paths.get(filePath), StandardCharsets.UTF_8)) 
	    {
	        stream.forEach(s -> contentBuilder.append(s).append("\n"));
	    }
	    catch (IOException e) 
	    {
	        e.printStackTrace();
	    }
	    return contentBuilder.toString();
	}*/
}

输出：

Root Element :: employees

=================================

Id : 101
FirstName : Lokesh
LastName : Gupta
country : India
Department Id : 25
Department Name : ITS
Id : 102
FirstName : Brian
LastName : Schultz
country : USA
Department Id : 26
Department Name : DEV

=================================

Employee Ids :: 101
Employee Ids :: 102
Employee First Name :: Lokesh
Employee First Name :: Brian

源代码下载

下载源码

学习愉快！

参考文献：

JDOM 网站

JDOM2 入门

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