在JAVA中最常用的解析xml的方式有四种，分别为：sax、dom、dom4j、jdom。sax方式的解析是基于事件的，比较适合大数据的解析，而dom的方式会将xml加载到内存中，构建出dom树，解析大文件时容易造成内存溢出，在实际开发中，我们应该选择最合适的解析方式。

假设我们有这样一个xml文件：

<xml>
   <userId><![CDATA[jianggujin]]></userId>
   <userName><![CDATA[蒋固金]]></userName>
   <birthday>1994-12-01</birthday>
</xml>

通过观察这段xml，我们可以将其抽象成一个实体类，取名为UserInfo。

import java.text.MessageFormat;

public class UserInfo
{
   private String userId;
   private String userName;
   private String birthday;

   public String getUserId()
   {
      return userId;
   }

   public void setUserId(String userId)
   {
      this.userId = userId;
   }

   public String getUserName()
   {
      return userName;
   }

   public void setUserName(String userName)
   {
      this.userName = userName;
   }

   public String getBirthday()
   {
      return birthday;
   }

   public void setBirthday(String birthday)
   {
      this.birthday = birthday;
   }

   @Override
   public String toString()
   {
      return MessageFormat.format("[userId:{0},userName:{1},birthday:{2}]",
            userId, userName, birthday);
   }
}

为了使用方便，将这段xml抽出来放在一个接口中，这样就不需要每个解析类里面都写一遍了，只需要实现这个接口就行了。

public interface XMLContent
{
   public String XML = "<xml><userId><![CDATA[jianggujin]]></userId><userName><![CDATA[蒋固金]]></userName><birthday>1994-12-01</birthday></xml>";
}

接下来，将演示四种方式解析xml的简单示例。

sax方式

sax方式需要一个解析的处理器，继承自org.xml.sax.helpers.DefaultHandler，
在DefaultHandler中，我们可能需要重写的方法有如下几个：

返回值	方法名	说明
void	startDocument()	接收文档开始的通知
void	startElement(String uri, String localName, String qName, Attributes attributes)	接收元素开始的通知
void	characters(char[] ch, int start, int length)	接收元素中字符数据的通知
void	endElement(String uri, String localName, String qName)	接收元素结束的通知
void	endDocument()	接收文档结束的通知

使用示例：

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;

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

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

/**
 * Sax解析XML
 * 
 * @author jianggujin
 * 
 */
public class SaxParser extends DefaultHandler implements XMLContent
{
   private UserInfo userInfo = null;
   private String currentTag = null;

   @Override
   public void startDocument() throws SAXException
   {
      userInfo = new UserInfo();
      System.out.println("startDocument...");
   }

   @Override
   public void startElement(String uri, String localName, String qName,
         Attributes attributes) throws SAXException
   {
      System.out.println("startElement...");
      currentTag = qName;
   }

   @Override
   public void characters(char[] ch, int start, int length) throws SAXException
   {
      System.out.println("characters...");
      String value = new String(ch, start, length);
      System.out.println(value);
      if ("userId".equals(currentTag))
      {
         userInfo.setUserId(value);
      }
      else if ("userName".equals(currentTag))
      {
         userInfo.setUserName(value);
      }
      else if ("birthday".equals(currentTag))
      {
         userInfo.setBirthday(value);
      }
   }

   @Override
   public void endElement(String uri, String localName, String qName)
         throws SAXException
   {
      System.out.println("endElement...");
      currentTag = null;
   }

   @Override
   public void endDocument() throws SAXException
   {
      System.out.println("endDocument...");
   }

   private UserInfo getUserInfo()
   {
      return userInfo;
   }

   public static UserInfo parse(InputStream inputStream) throws SAXException,
         ParserConfigurationException, IOException
   {
      XMLReader reader = SAXParserFactory.newInstance().newSAXParser()
            .getXMLReader();
      SaxParser handler = new SaxParser();
      reader.setContentHandler(handler);
      reader.parse(new InputSource(inputStream));
      return handler.getUserInfo();
   }

   public static UserInfo parse(String xml) throws SAXException,
         ParserConfigurationException, IOException
   {
      return parse(new ByteArrayInputStream(xml.getBytes("UTF-8")));
   }

   public static void main(String[] args) throws Exception
   {
      System.out.println(parse(XML));
   }
}

DOM方式

import java.io.ByteArrayInputStream;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;

/**
 * Dom方式解析XML
 * 
 * @author jianggujin
 * 
 */
public class DomParser implements XMLContent
{

   public static void main(String[] args) throws Exception
   {
      DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
      DocumentBuilder builder = factory.newDocumentBuilder();
      Document document = builder.parse(new ByteArrayInputStream(XML
            .getBytes("UTF-8")));
      UserInfo userInfo = new UserInfo();
      userInfo.setUserId(document.getElementsByTagName("userId").item(0)
            .getTextContent());
      userInfo.setUserName(document.getElementsByTagName("userName").item(0)
            .getTextContent());
      userInfo.setBirthday(document.getElementsByTagName("birthday").item(0)
            .getTextContent());
      System.out.println(userInfo);
   }
}

DOM4j方式

import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;

/**
 * Dom4d方式解析XML
 * 
 * @author jianggujin
 * 
 */
public class Dom4jParser implements XMLContent
{

   public static void main(String[] args) throws Exception
   {
      Document document = DocumentHelper.parseText(XML);
      Element rootElement = document.getRootElement();

      UserInfo userInfo = new UserInfo();
      userInfo.setUserId(rootElement.elementText("userId"));
      userInfo.setUserName(rootElement.elementText("userName"));
      userInfo.setBirthday(rootElement.elementText("birthday"));
      System.out.println(userInfo);
   }
}

jDOM方式

import java.io.ByteArrayInputStream;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.input.SAXBuilder;

/**
 * JDom方式解析XML
 * 
 * @author jianggujin
 * 
 */
public class JDomParser implements XMLContent
{
   public static void main(String[] args) throws Exception
   {
      SAXBuilder builder = new SAXBuilder();
      Document document = builder.build(new ByteArrayInputStream(XML
            .getBytes("UTF-8")));
      Element rootElement = document.getRootElement();

      UserInfo userInfo = new UserInfo();
      userInfo.setUserId(rootElement.getChildText("userId"));
      userInfo.setUserName(rootElement.getChildText("userName"));
      userInfo.setBirthday(rootElement.getChildText("birthday"));
      System.out.println(userInfo);
   }
}

JAVA解析XML