前言
XML現(xiàn)在已經(jīng)成為一種通用的數(shù)據(jù)交換格式,它的平臺無關(guān)性,語言無關(guān)性,系統(tǒng)無關(guān)性,給數(shù)據(jù)集成與交互帶來了極大的方便。對于XML本身的語法知識與技術(shù)細(xì)節(jié),需要閱讀相關(guān)的技術(shù)文獻(xiàn),這里面包括的內(nèi)容有DOM(Document Object Model)、DTD(Document Type Definition)、SAX(Simple API for XML)、XSD(Xml Schema Definition)、XSLT(Extensible Stylesheet Language Transformations)，具體可參閱w3c官方網(wǎng)站文檔獲取更多信息。XML在不同的語言里解析方式都是一樣的,只不過實(shí)現(xiàn)的語法不同而已。基本的解析方式有兩種,一種叫SAX，另一種叫DOM。
DOM
DOM生成和解析XML文檔為 XML 文檔的已解析版本定義了一組接口。解析器讀入整個(gè)文檔，然后構(gòu)建一個(gè)駐留內(nèi)存的樹結(jié)構(gòu)，然后代碼就可以使用 DOM 接口來操作這個(gè)樹結(jié)構(gòu)。優(yōu)點(diǎn)：整個(gè)文檔樹在內(nèi)存中，便于操作；支持刪除、修改、重新排列等多種功能；缺點(diǎn)：將整個(gè)文檔調(diào)入內(nèi)存（包括無用的節(jié)點(diǎn)），浪費(fèi)時(shí)間和空間；使用場合：一旦解析了文檔還需多次訪問這些數(shù)據(jù)；硬件資源充足（內(nèi)存、CPU）。
/**
* DOM生成與解析XML文檔
*/
public class DomDemo implements XmlDocument {
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("活這么大就沒飽過"));
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("24"));
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("解析完畢");
} 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());
}
}
}
SAX
SAX生成和解析XML文檔為解決DOM的問題，出現(xiàn)了SAX。SAX ，事件驅(qū)動(dòng)。當(dāng)解析器發(fā)現(xiàn)元素開始、元素結(jié)束、文本、文檔的開始或結(jié)束等時(shí)，發(fā)送事件，程序員編寫響應(yīng)這些事件的代碼，保存數(shù)據(jù)。優(yōu)點(diǎn)：不用事先調(diào)入整個(gè)文檔，占用資源少；SAX解析器代碼比DOM解析器代碼小，適于Applet，下載。缺點(diǎn)：不是持久的；事件過后，若沒保存數(shù)據(jù)，那么數(shù)據(jù)就丟了；無狀態(tài)性；從事件中只能得到文本，但不知該文本屬于哪個(gè)元素；使用場合：Applet;只需XML文檔的少量內(nèi)容，很少回頭訪問；機(jī)器內(nèi)存少。
/**
* SAX文檔解析
*/
public class SaxDemo implements XmlDocument {
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();
}
}
}
class MySAXHandler extends DefaultHandler {
boolean hasAttribute = false;
Attributes attributes = null;
public void startDocument() throws SAXException {
System.out.println("文檔開始打印了");
}
public void endDocument() throws SAXException {
System.out.println("文檔打印結(jié)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));
}
}
DOM4J
DOM4J生成和解析XML文檔DOM4J 是一個(gè)非常非常優(yōu)秀的Java XML API，具有性能優(yōu)異、功能強(qiáng)大和極端易用使用的特點(diǎn)，同時(shí)它也是一個(gè)開放源代碼的軟件。如今你可以看到越來越多的 Java 軟件都在使用 DOM4J 來讀寫 XML，特別值得一提的是連 Sun 的 JAXM 也在用 DOM4J。
/**
* Dom4j 生成XML文檔與解析XML文檔
*/
public class Dom4jDemo implements XmlDocument {
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("活這么大就沒飽過");
Element sex = employee.addElement("sex");
sex.setText("m");
Element age = employee.addElement("age");
age.setText("24");
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");
}
}
JDOM
JDOM生成和解析XML 為減少DOM、SAX的編碼量，出現(xiàn)了JDOM；優(yōu)點(diǎn)：20-80原則，極大減少了代碼量。使用場合：要實(shí)現(xiàn)的功能簡單，如解析、創(chuàng)建等，但在底層，JDOM還是使用SAX（最常用）、DOM、Xanan文檔。
/**
* JDOM 生成與解析XML文檔 *
*/
public class JDomDemo implements XmlDocument {
public void createXml(String fileName) {
Document document;
Element root;
root = new Element("employees");
document = new Document(root);
Element employee = new Element("employee");
root.addContent(employee);
Element name = new Element("name");
name.setText("活這么大就沒飽過");
employee.addContent(name);
Element sex = new Element("sex");
sex.setText("m");
employee.addContent(sex);
Element age = new Element("age");
age.setText("24");
employee.addContent(age);
XMLOutputter XMLOut = new XMLOutputter();
try {
XMLOut.output(document, new FileOutputStream(fileName));
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public void parserXml(String fileName) {
SAXBuilder builder = new SAXBuilder(false);
try {
Document document = builder.build(fileName);
Element employees = document.getRootElement();
List employeeList = employees.getChildren("employee");
for (int i = 0; Element employee = (Element) employeeList.get(i);
List employeeInfo = employee.getChildren();
for (int j = 0; System.out.println(((Element) employeeInfo.get(j)).getName() + ":" + ((Element) employeeInfo.get(j)).getValue());
} catch (JDOMException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
總結(jié)
這篇博客介紹了 Java 語言編寫的4種解析 XML 文件的工具代碼，大家可以根據(jù)自己的業(yè)務(wù)需求選擇具體的方案并進(jìn)行自定義場景使用，就 XML 解析而言，我個(gè)人推薦選擇 DOM4J 的形式，但是現(xiàn)在儲存數(shù)據(jù)的格式種類繁多，而 XML 是我最不推薦的形式，推薦大家使用 JSON、YAML 等數(shù)據(jù)格式。
