XML是一种可扩展标记语言
以下是一个完整的XML文件（也是下文介绍读写XML的样本）：
<?xml version="1.0" encoding="UTF-8"?
> <poem author="William Carlos Williams" title="The Great Figure"> <line>Among the rain</line> <line>and ligths</line> <line>I saw the figure 5</line> <line>in gold</line> <line>on a red</line> <line>fire truck</line> <line>moving</line> <line>tense</line> <line>unheeded</line> <line>to gong clangs</line> <line>siren howls</line> <line>and wheels rumbling</line> <line>through the dark city</line> </poem>
一、写XML
本文介绍两种方式：使用DOM开发包来写XML文件和用String对象的方式
将Poem类作为数据源，提供须要转换成XML的内容：
class Poem {
private static String title = "The Great Figure";
private static String author = "William Carlos Williams";
private static ArrayList<String> lines = new ArrayList<String>();
static {
lines.add("Among the rain");
lines.add("and ligths");
lines.add("I saw the figure 5");
lines.add("in gold");
lines.add("on a red");
lines.add("fire truck");
lines.add("moving");
lines.add("tense");
lines.add("unheeded");
lines.add("to gong clangs");
lines.add("siren howls");
lines.add("and wheels rumbling");
lines.add("through the dark city");
}
public static String getTitle() {
return title;
}
public static String getAuthor() {
return author;
}
public static ArrayList<String> getLines() {
return lines;
}
}
1、用DOM写XML文件
流程：
（1）创建一个空的Document对象（最顶层的DOM对象，包括了创建XML所须要的其它一切）。
（2）创建元素和属性，把元素和属性加到Document对象中。
（3）把Document对象的内容转换成String对象。
（4）把String对象写到目标文件中去。
import java.util.ArrayList;
import java.io.*;
import javax.xml.parsers.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.*;
public class XmlTest {
public static void main(String[] args) {
Document doc = createXMLContent1(); // 创建空文档
createElements(doc); // 创建XML
String xmlContent = createXMLString(doc);// 创建字符串以表示XML
writeXMLToFile1(xmlContent);
}
/*********** 用DOM写XML文件 ***********/
private static Document createXMLContent1() {
Document doc = null;
try {
// 使应用程序可以从XML文档获取生成 DOM 对象树的解析器
DocumentBuilderFactory dbfac = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder = dbfac.newDocumentBuilder();
doc = docBuilder.newDocument();
// 作为 XML 声明 的一部分指定此文档是否是单独的的属性。未指定时，此属性为 false。
doc.setXmlStandalone(true);
} catch (ParserConfigurationException pce) {
System.out.println("Couldn't create a DocumentBuilder");
System.exit(1);
}
return doc;
}
private static void createElements(Document doc) {
// 创建根元素
Element poem = doc.createElement("poem");
poem.setAttribute("title", Poem.getTitle());
poem.setAttribute("author", Poem.getAuthor());
// 把根元素加到文档里去
doc.appendChild(poem);
// 创建子元素
for (String lineIn : Poem.getLines()) {
Element line = doc.createElement("line");
Text lineText = doc.createTextNode(lineIn);
line.appendChild(lineText);
// 把每一个元素加到根元素里去
poem.appendChild(line);
}
}
private static String createXMLString(Document doc) {
// 将DOM转换成字符串
Transformer transformer = null;
StringWriter stringWriter = new StringWriter();
try {
TransformerFactory transformerFactory = TransformerFactory.newInstance();
transformer = transformerFactory.newTransformer();
// 是否应输出 XML 声明
transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
// 是否以XML格式自己主动换行
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
// 创建字符串以包括XML
stringWriter = new StringWriter();
StreamResult result = new StreamResult(stringWriter);// 充当转换结果的持有者
DOMSource source = new DOMSource(doc);
transformer.transform(source, result);
} catch (TransformerConfigurationException e) {
System.out.println("Couldn't create a Transformer");
System.exit(1);
} catch (TransformerException e) {
System.out.println("Couldn't transforme DOM to a String");
System.exit(1);
}
return stringWriter.toString();
}
private static void writeXMLToFile1(String xmlContent) {
String fileName = "E:\test\domoutput.xml";
try {
File domOutput = new File(fileName);
FileOutputStream domOutputStream = new FileOutputStream(domOutput);
domOutputStream.write(xmlContent.getBytes());
domOutputStream.close();
System.out.println(fileName + " was successfully written");
} catch (FileNotFoundException e) {
System.out.println("Couldn't find a file called" + fileName);
System.exit(1);
} catch (IOException e) {
System.out.println("Couldn't write a file called" + fileName);
System.exit(1);
}
}
2、用String写XML文件
这样的方法就比較简单。就是直接用字符串把整个XML文件描写叙述出来，然后保存文件。
二、读取XML文件
两种方式：用DOM读取XML文件和用SAX方式。一般DOM处理内容比較小的XML文件。而SAX能够处理随意大小的XML文件。
1、用DOM读取XML文件
public class XmlTest {
public static void main(String[] args) {
String fileName = "E:\test\domoutput.xml";
writeFileContentsToConsole(fileName);
}
/*********** 用DOM读取XML文件 ***********/
private static void writeFileContentsToConsole(String fileName) {
Document doc = createDocument(fileName);
Element root = doc.getDocumentElement();// 获取根元素
StringBuilder sb = new StringBuilder();
sb.append("The root element is named:"" + root.getNodeName() + """);
sb.append("and has the following attributes: ");
NamedNodeMap attributes = root.getAttributes();
for (int i = 0; i < attributes.getLength(); i++) {
Node thisAttribute = attributes.item(i);
sb.append(thisAttribute.getNodeName());
sb.append("("" + thisAttribute.getNodeValue() + "")");
if (i < attributes.getLength() - 1) {
sb.append(",");
}
}
System.out.println(sb);// 根元素的描写叙述信息
NodeList nodes = doc.getElementsByTagName("line");
for (int i = 0; i < nodes.getLength(); i++) {
Element element = (Element) nodes.item(i);
System.out.println("Found an element named ""
+ element.getTagName() + """
+ "With the following content: ""
+ element.getTextContent() + """);
}
}
private static Document createDocument(String fileName) {// 从文件创建DOM的Document对象
Document doc = null;
try {
File xmlFile = new File(fileName);
DocumentBuilderFactory dbfac = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder = dbfac.newDocumentBuilder();
doc = docBuilder.parse(xmlFile);// 解析xml文件载入为dom文档
doc.setXmlStandalone(true);
} catch (IOException e) {
e.printStackTrace();
} catch (SAXException e) {
e.printStackTrace();
} catch (ParserConfigurationException e) {
e.printStackTrace();
}
return doc;
}
}/*
* Output:
* The root element is named:"poem"and has the following attributes: author("William Carlos Williams"),title("The Great Figure")
* Found an element named "line"With the following content: "Among the rain"
* Found an element named "line"With the following content: "and ligths"
* ... ...
*/// :~
2、用SAX读取XML文件
SAX是使用ContentHandler接口来公开解析事件，并且SAX包提供了一个默认实现类DefaultHandler，它的默认行为就是什么都不做。以下就通过XMLToConsoleHandler类来覆盖当中的一些方法，来捕获XML文件的内容。
import org.w3c.dom.CharacterData;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
public class XmlTest {
public static void main(String[] args) {
String fileName = "E:\test\domoutput.xml";
getFileContents(fileName);
}
private static void getFileContents(String fileName) {
try {
XMLToConsoleHandler handler = new XMLToConsoleHandler();
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser saxParser = factory.newSAXParser();
saxParser.parse(fileName, handler);
} catch (IOException e) {
e.printStackTrace();
} catch (ParserConfigurationException e) {
e.printStackTrace();
} catch (SAXException e) {
e.printStackTrace();
}
}
}
/*********** 用SAX读取XML文件 ***********/
class XMLToConsoleHandler extends DefaultHandler {
public void characters(char[] content, int start, int length)
throws SAXException { // 处理元素的真正内容
System.out.println("Found content: " + new String(content, start, length));
}
public void endElement(String arg0, String localName, String qName)throws SAXException {
System.out.println("Found the end of an element named "" + qName + """);
}
public void startElement(String uri, String localName, String qName,
Attributes attributes) throws SAXException {
StringBuilder sb = new StringBuilder();
sb.append("Found the start of an element named "" + qName + """);
if (attributes != null && attributes.getLength() > 0) {
sb.append(" with attributes named ");
for (int i = 0; i < attributes.getLength(); i++) {
String attributeName = attributes.getLocalName(i);
String attributeValue = attributes.getValue(i);
sb.append(""" + attributeName + """);
sb.append(" (value = ");
sb.append(""" + attributeValue + """);
sb.append(")");
if (i < attributes.getLength() - 1) {
sb.append(",");
}
}
}
System.out.println(sb.toString());
}
}