JDOM 解析器可用于读取 XML、解析 xml 并在更新内容后写入 XML 文件。
它将 JDOM2 文档存储在内存中以读取和修改它的值。

JDOM2 Maven 依赖

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

要执行 XPath，我们还需要 jaxen。

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

创建 JDOM2 文档

我们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。

• 使用 DOM 解析器

private static Document getDOMParsedDocument(final String fileName) 
{
	Document document = null;
	try 
	{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		
        //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;
}

• 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;
}

• 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;
}

使用 XPath 读取 XML 内容

要使用 xpath 读取任何一组元素的值，我们需要编译 XPathExpression并使用它的 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());
}

读取和过滤 XML 内容

我们将使用下面的 employees.xml文件进行测试。

<employees>
	<employee id="101">
		<firstName>JackLi</firstName>
		<lastName>Li</lastName>
		<country>Netherlands</country>
		<department id="15">
			<name>HR</name>
		</department>
	</employee>
	<employee id="102">
		<firstName>BobRobert</firstName>
		<lastName>Ma</lastName>
		<country>USA</country>
		<department id="16">
			<name>Man</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());
}

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"));
}

读取元素值

使用 Element.getChildText()或者 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"));
}