# Java JDOM2 – XML 讀取示例 > 原文： [https://howtodoinjava.com/xml/jdom2-read-parse-xml-examples/](https://howtodoinjava.com/xml/jdom2-read-parse-xml-examples/) **JDOM 解析器**可用于在更新 XML 內容后用于讀取 XML，解析 XML 和寫入 XML 文件。 它將 **JDOM2 文檔**存儲在內存中，以讀取和修改其值。 將 XML 文檔加載到內存中后，JDOM2 維護嚴格的父子類型關系。 父類型的 JDOM 實例（父）具有訪問其內容的方法，子類型的 JDOM 實例（內容）具有訪問其父對象的方法。 ```java Table of Contents Project Structure JDOM2 Maven Dependency Create JDOM2 Document Read and filter XML content Read XML Content with XPath Complete Example 源碼下載 ``` ## 項目結構 請創建此文件夾結構以執行示例。 這是在 Eclipse 中創建的[簡單 Maven 項目](//howtodoinjava.com/maven/create-a-simple-java-project-using-maven/)。  項目結構 請注意，我已經使用了 [lambda 表達式](//howtodoinjava.com/java8/complete-lambda-expressions-tutorial-in-java/)和[方法引用](//howtodoinjava.com/java8/lambda-method-references-example/)，因此您需要配置為使用 JDK 1.8。 ## JDOM2 Maven 依賴關系 ```java <dependency> <groupId>org.jdom</groupId> <artifactId>jdom2</artifactId> <version>2.0.6</version> </dependency> ``` 要執行 XPath，您還需要 jaxen。 ```java <dependency> <groupId>jaxen</groupId> <artifactId>jaxen</artifactId> <version>1.1.6</version> </dependency> ``` ## 創建 JDOM2 文檔 您可以使用下面列出的任何解析器創建`org.jdom2.Document`實例。 它們都解析 XML 并返回**內存中的 JDOM 文檔**。 1. #### 使用 DOM 解析器 ```java 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 ```java 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 ```java 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; } ``` ## 讀取和過濾 XML 內容 我將讀取`employees.xml`文件。 ```java <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> ``` #### 讀取根節點 使用`document.getRootElement()`方法。 ```java 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()); } ``` 輸出： ```java Root Element :: employees ``` #### 讀取屬性值 使用`Element.getAttributeValue()`方法。 ```java 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")); } ``` 輸出： ```java Id : 101 Id : 102 ``` #### 讀取元素值 使用`Element.getChildText()`或`Element.getText()`方法。 ```java 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: ```java 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 讀取 XML 內容 要使用 [xpath](//howtodoinjava.com/xml/how-to-work-with-xpaths-in-java-with-examples/) 讀取任何元素的值集，您需要編譯`XPathExpression`并使用其`evaluate()`方法。 ```java 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()); } ``` 輸出： ```java Employee Ids :: 101 Employee Ids :: 102 Employee First Name :: Lokesh Employee First Name :: Brian ``` ## 完整的 JDOM2 XML 讀取示例 這是在 Java 中使用 JDOM2 **讀取 xml 的完整代碼**。 ```java 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(); }*/ } ``` 輸出： ```java 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 ``` ## 源代碼下載 [下載源碼](//howtodoinjava.com/wp-content/downloads/JDOM2Examples.zip) 學習愉快！ 參考文獻： [JDOM 網站](http://www.jdom.org/) [JDOM2 入門](https://github.com/hunterhacker/jdom/wiki/JDOM2-A-Primer)