XML-SAX

XML解析技术常用的就是DOM和SAX，DOM(Document Object Model)即文档对象模型，将xml文件整体解析为内存中的特定数据结构，然后再对该内存中的数据机构进行操作（增删改查），SAX(Simple API for XML)即简单XML API，以流的方式读取xml文档，并以事件驱动来处理节点，其只能查询，无法对xml进行更新操作。

DOM4J是借助SAX方式来构建DOM对象，jdk中自带的DOM（com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl）的API是w3c标准API，DOM4J则是自己独有的一套API，二者的内在实现也略有不同，jdk的DOM需要将xml全部读入内存再进行解析，DOM4J则使用SAX进行流式解析（事件驱动）。

 <?xml version="1.0" encoding="UTF-8"?>
 <DocumentElement param="value">
     <FirstElement>
         &#xb6; Some Text
     </FirstElement>
     <?some_pi some_attr="some_value"?>
     <SecondElement param2="something">
         Pre-Text <Inline>Inlined text</Inline> Post-text.
     </SecondElement>
</DocumentElement>

SAX会这样解析上面的xml文件：

• XML Element start, named DocumentElement, with an attribute param equal to "value"
• XML Element start, named FirstElement
• XML Text node, with data equal to "¶ Some Text" (note: certain white spaces can be changed)
• XML Element end, named FirstElement
• Processing Instruction event, with the target some_pi and data some_attr="some_value" (the content after the target is just text; however, it is very common to imitate the syntax of XML attributes, as in this example)
• XML Element start, named SecondElement, with an attribute param2 equal to "something"
• XML Text node, with data equal to "Pre-Text"
• XML Element start, named Inline
• XML Text node, with data equal to "Inlined text"
• XML Element end, named Inline
• XML Text node, with data equal to "Post-text."
• XML Element end, named SecondElement
• XML Element end, named DocumentElement

下面就使用SAX对一个spring配置文件简单解析。

spring配置文件

<spring:beans xmlns:spring="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
  <spring:bean id="myBean" class="com.zyong.spring.beanfactory.MyBean"/>
</spring:beans>

测试方法：

String file = ClassLoader.getSystemResource("spring/spring-test.xml").getFile();
com.sun.org.apache.xerces.internal.parsers.SAXParser saxParser = new com.sun.org.apache.xerces.internal.parsers.SAXParser();
saxParser.setContentHandler(new MyHandler());
saxParser.parse(new InputSource(file));

事件处理器：

private class MyHandler extends DefaultHandler {

  @Override
  public void startDocument() throws SAXException {
    System.out.println("start document -> parse begin");
  }

  @Override
  public void endDocument() throws SAXException {
        System.out.println("end document -> parse finished");
  }

  @Override
  public void startElement(String uri, String localName, String qName,
                           Attributes attributes) throws SAXException {
    System.out.println("start element-----------");
    System.out.println("    localName: " + localName);
    System.out.println("    qName: " + qName);
  }

  @Override
  public void characters(char[] ch, int start, int length)
          throws SAXException {
    System.out.println("characters-----------");
    System.out.println("    ch: " + ch);
    System.out.println("    start: " + start);
    System.out.println("    length: " + length);
  }

  @Override
  public void endElement(String uri, String localName, String qName)
          throws SAXException {
    System.out.println("end element-----------");
    System.out.println("    localName: " + localName);
    System.out.println("    qName: " + qName);

  }
}

输出：

start document -> parse begin
start element-----------
    localName: beans
    qName: spring:beans
characters-----------
    ch: [C@4cc77c2e
    start: 272
    length: 5
start element-----------
    localName: bean
    qName: spring:bean
end element-----------
    localName: bean
    qName: spring:bean
characters-----------
    ch: [C@4cc77c2e
    start: 348
    length: 5
start element-----------
    localName: bean
    qName: spring:bean
end element-----------
    localName: bean
    qName: spring:bean
characters-----------
    ch: [C@4cc77c2e
    start: 436
    length: 1
end element-----------
    localName: beans
    qName: spring:beans
end document -> parse finished

参考：http://blog.csdn.net/u011179993/article/details/47415603

　　http://www.cnblogs.com/mengdd/archive/2013/06/02/3114177.html