Java XML解析

XML作为一种通用的数据格式，其平台无关性、语言无关性，给数据集成和交互带来了极大的方便。对于XML本身的语法知识与技术细节，可以参考w3c官方文档。

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。起基本的解析方式有两种，一种是SAX，一种是DOM。SAX是基于事件流的解析，DOM是基于XML文档书结构的解析。

示例XML 文件

<?xml version="1.0" encoding="UTF-8"?>
<employees>
<employee>
<name>Xu Dong</name>
<sex>M</sex>
<age>30</age>
</employee>
<employee>
<name>Huan Yun</name>
<sex>Y</sex>
<age>24</age>
</employee>
</employees>

使用Java语言来实现DOM与SAX的XML文档的生成与解析。

首先定义一个操作xml文档的接口，定义了XML的建立与解析。XMLUtils

package com.hugo.huan;

/**
* @author xudong.zh
* XML文档建立与解析的接口
*/
public interface XMLUtils {

/**
* 建立XML文档
* @param fileName 文件全路径名称
*/
public void createXml(String fileName);

/**
* 解析XML文档
* @param fileName 文件全路径名称
*/
public void parserXml(String fileName);
}

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。

此方法的优点：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）。

package com.hugo.huan;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

/**
* DOM生成与解析XML文档
*
* @author hugo
*
*/
public class XMLDom implements XMLUtils {

private Document document;
private String fileName;

/**
* 初始化，建立document
*/
public void init() {
try {
DocumentBuilderFactory factory = DocumentBuilderFactory
.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
document = builder.newDocument();
} catch (ParserConfigurationException e) {
System.out.println(e.getMessage());
}
}

public void createXml(String fileName) {
Element root = document.createElement("employees");
document.appendChild(root);
Element employee = document.createElement("employee");
Element name = document.createElement("name");
name.appendChild(document.createTextNode("职员"));
employee.appendChild(name);
Element sex = document.createElement("sex");
sex.appendChild(document.createTextNode("M"));
employee.appendChild(sex);
Element age = document.createElement("age");
age.appendChild(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");
//编码格式，必须使用gb2312， 经测试，JDK6 GBK不支持，UTF8也报错了
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();
System.out.println("Employees"+ employees.getLength());
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();
System.out.println(j+ "j" + employeeMeta.getLength());
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());
}
}

public static void main (String [] args){
XMLDom  dom = new XMLDom();
dom.init();
//dom.createXml("create.xml");

dom.parserXml("create.xml");
}
}

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；

package com.hugo.huan;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

/**
* SAX 生成和解析XML
*
* @author hugo
*
*/
public class XMLSax implements XMLUtils {

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 static void main (String args[]){
XMLSax sax = new XMLSax();
sax.parserXml("create.xml");

}
}

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));
}

}

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。

package com.hugo.huan;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.Iterator;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;

/**
*
* @author Dom4j 生成XML文档与解析XML文档
*/
public class Dom4jDemo implements XMLUtils{

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("Xu Dong");
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.setProperty(arg0, arg1);
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");
}

public static void main(String args[]){
Dom4jDemo dom = new Dom4jDemo();
//dom.createXml("dom4j.xml");
dom.parserXml("dom4j.xml");
}
}

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。

package com.hugo.huan;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.List;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.JDOMException;
import org.jdom2.input.SAXBuilder;
import org.jdom2.output.XMLOutputter;

/**
*
* @author JDOM 生成与解析XML文档
*
*/
public class JDomDemo implements XMLUtils {

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("ddvip");
employee.addContent(name);
Element sex = new Element("sex");
sex.setText("m");
employee.addContent(sex);
Element age = new Element("age");
age.setText("23");
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<Element> employeeList = employees.getChildren("employee");
for (Element employee : employeeList) {
List<Element> employeeInfoList = employee.getChildren();
for (Element employeeInfo : employeeInfoList) {
System.out.println(employeeInfo.getName() + ":"
+ employeeInfo.getValue());
}
}
} catch (JDOMException e) {
e.printStackTrace();
} catch (IOException e) {

e.printStackTrace();
}
}

public static void main(String args[]){
JDomDemo dom = new JDomDemo();
// dom.createXml("jdom2.xml");
dom.parserXml("create.xml");
}
}