Java解析XML的四种方法

XML现在已经成为一种通用的数据交换格式,它的平台无关性,语言无关性,系统无关性,给数据集成与交互带来了极大的方便。这里面包括的内容有DOM(Document Object Model),DTD(Document Type Definition),SAX(Simple API for XML),XSD(Xml Schema Definition),XSLT(Extensible Stylesheet Language Transformations)。

XML在不同的语言里解析方式都是一样的,只不过实现的语法不同而已。基本的解析方式有两种,一种叫SAX，另一种叫DOM。SAX是基于事件流的解析,DOM是基于XML文档树结构的解析。假设我们XML的内容和结构如下:

<?xml version="1.0" encoding="UTF-8"?> <employees> <employee> <name>ddviplinux</name> <sex>m</sex> <age>30</age> </employee> </employees>

1.DOM生成和解析XML文档
为 XML 文档的已解析版本定义了一组接口。解析器读入整个文档，然后构建一个驻留内存的树结构，然后代码就可以使用 DOM 接口来操作这个树结构。优点：整个文档树在内存中，便于操作；支持删除、修改、重新排列等多种功能；缺点：将整个文档调入内存（包括无用的节点），浪费时间和空间；使用场合：一旦解析了文档还需多次访问这些数据；硬件资源充足（内存、CPU）。

public class DomDemo {private Document document;private String fileName;public void init() {try {DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();DocumentBuilder builder = factory.newDocumentBuilder();this.document = builder.newDocument();} catch (ParserConfigurationException e) {System.out.println(e.getMessage());}}public void createXml(String fileName) {Element root = this.document.createElement("employees");this.document.appendChild(root);Element employee = this.document.createElement("employee");Element name = this.document.createElement("name");name.appendChild(this.document.createTextNode("丁宏亮"));employee.appendChild(name);Element sex = this.document.createElement("sex");sex.appendChild(this.document.createTextNode("m"));employee.appendChild(sex);Element age = this.document.createElement("age");age.appendChild(this.document.createTextNode("30"));employee.appendChild(age);root.appendChild(employee);TransformerFactory tf = TransformerFactory.newInstance();try {Transformer transformer = tf.newTransformer();DOMSource source = new DOMSource(document);transformer.setOutputProperty(OutputKeys.ENCODING, "gb2312");transformer.setOutputProperty(OutputKeys.INDENT, "yes");PrintWriter pw = new PrintWriter(new FileOutputStream(fileName));StreamResult result = new StreamResult(pw);transformer.transform(source, result);System.out.println("生成XML文件成功!");} catch (TransformerConfigurationException e) {System.out.println(e.getMessage());} catch (IllegalArgumentException e) {System.out.println(e.getMessage());} catch (FileNotFoundException e) {System.out.println(e.getMessage());} catch (TransformerException e) {System.out.println(e.getMessage());}}public void parserXml(String fileName) {try {DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();DocumentBuilder db = dbf.newDocumentBuilder();Document document = db.parse(fileName);NodeList employees = document.getChildNodes();for (int i = 0; i < employees.getLength(); i++) {Node employee = employees.item(i);NodeList employeeInfo = employee.getChildNodes();for (int j = 0; j < employeeInfo.getLength(); j++) {Node node = employeeInfo.item(j);NodeList employeeMeta = node.getChildNodes();for (int k = 0; k < employeeMeta.getLength(); k++) {System.out.println(employeeMeta.item(k).getNodeName()+ ":" + employeeMeta.item(k).getTextContent());}}}System.out.println("解析完毕");} catch (FileNotFoundException e) {System.out.println(e.getMessage());} catch (ParserConfigurationException e) {System.out.println(e.getMessage());} catch (SAXException e) {System.out.println(e.getMessage());} catch (IOException e) {System.out.println(e.getMessage());}}}

2.SAX生成和解析XML文档
为解决DOM的问题，出现了SAX。SAX ，事件驱动。当解析器发现元素开始、元素结束、文本、文档的开始或结束等时，发送事件，程序员编写响应这些事件的代码，保存数据。优点：不用事先调入整个文档，占用资源少；SAX解析器代码比DOM解析器代码小，适于Applet，下载。缺点：不是持久的；事件过后，若没保存数据，那么数据就丢了；无状态性；从事件中只能得到文本，但不知该文本属于哪个元素；使用场合：Applet;只需XML文档的少量内容，很少回头访问；机器内存少；

public class SaxDemo{ public void createXml(String fileName) { System.out.println("<<"+fileName+">>"); } public void parserXml(String fileName) { SAXParserFactory saxfac = SAXParserFactory.newInstance(); try { SAXParser saxparser = saxfac.newSAXParser(); InputStream is = new FileInputStream(fileName); saxparser.parse(is, new MySAXHandler()); } catch (ParserConfigurationException e) { e.printStackTrace(); } catch (SAXException e) { e.printStackTrace(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } public class MySAXHandler extends DefaultHandler {boolean hasAttribute = false;Attributes attributes = null;public void startDocument() throws SAXException {System.out.println("文档开始打印了");}public void endDocument() throws SAXException {System.out.println("文档打印结束了");}public void startElement(String uri, String localName, String qName,Attributes attributes) throws SAXException {if (qName.equals("employees")) {return;}if (qName.equals("employee")) {System.out.println(qName);}if (attributes.getLength() > 0) {this.attributes = attributes;this.hasAttribute = true;}}public void endElement(String uri, String localName, String qName)throws SAXException {if (hasAttribute && (attributes != null)) {for (int i = 0; i < attributes.getLength(); i++) {System.out.println(attributes.getQName(0)+ attributes.getValue(0));}}}public void characters(char[] ch, int start, int length)throws SAXException {System.out.println(new String(ch, start, length));}}

3.DOM4J生成和解析XML文档
DOM4J 是一个非常非常优秀的Java XML API，具有性能优异、功能强大和极端易用使用的特点，同时它也是一个开放源代码的软件。如今你可以看到越来越多的 Java 软件都在使用 DOM4J 来读写 XML，特别值得一提的是连 Sun 的 JAXM 也在用 DOM4J。

public class Dom4jDemo {public void createXml(String fileName) {Document document = DocumentHelper.createDocument();Element employees = document.addElement("employees");Element employee = employees.addElement("employee");Element name = employee.addElement("name");name.setText("ddvip");Element sex = employee.addElement("sex");sex.setText("m");Element age = employee.addElement("age");age.setText("29");try {Writer fileWriter = new FileWriter(fileName);XMLWriter xmlWriter = new XMLWriter(fileWriter);xmlWriter.write(document);xmlWriter.close();} catch (IOException e) {System.out.println(e.getMessage());}}public void parserXml(String fileName) {File inputXml = new File(fileName);SAXReader saxReader = new SAXReader();try {Document document = saxReader.read(inputXml);Element employees = document.getRootElement();for (Iterator i = employees.elementIterator(); i.hasNext();) {Element employee = (Element) i.next();for (Iterator j = employee.elementIterator(); j.hasNext();) {Element node = (Element) j.next();System.out.println(node.getName() + ":" + node.getText());}}} catch (DocumentException e) {System.out.println(e.getMessage());}System.out.println("dom4j parserXml");}}

4.JDOM生成和解析XML
为减少DOM、SAX的编码量，出现了JDOM；优点：20-80原则，极大减少了代码量。使用场合：要实现的功能简单，如解析、创建等，但在底层，JDOM还是使用SAX（最常用）、DOM、Xanan文档。

public class Dom4jDemo {public void createXml(String fileName) {Document document = DocumentHelper.createDocument();Element employees = document.addElement("employees");Element employee = employees.addElement("employee");Element name = employee.addElement("name");name.setText("ddvip");Element sex = employee.addElement("sex");sex.setText("m");Element age = employee.addElement("age");age.setText("29");try {Writer fileWriter = new FileWriter(fileName);XMLWriter xmlWriter = new XMLWriter(fileWriter);xmlWriter.write(document);xmlWriter.close();} catch (IOException e) {System.out.println(e.getMessage());}}public void parserXml(String fileName) {File inputXml = new File(fileName);SAXReader saxReader = new SAXReader();try {Document document = saxReader.read(inputXml);Element employees = document.getRootElement();for (Iterator i = employees.elementIterator(); i.hasNext();) {Element employee = (Element) i.next();for (Iterator j = employee.elementIterator(); j.hasNext();) {Element node = (Element) j.next();System.out.println(node.getName() + ":" + node.getText());}}} catch (DocumentException e) {System.out.println(e.getMessage());}System.out.println("dom4j parserXml");}}