Java基础学习总结（10）——JAVA解析XML

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[张三]]></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voidstartDocument()接收文档开始的通知voidstartElement(String uri, String localName, String qName, Attributes attributes)接收元素开始的通知voidcharacters(char[] ch, int start, int length)接收元素中字符数据的通知voidendElement(String uri, String localName, String qName)接收元素结束的通知voidendDocument()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);   }}