Sax 是事件驱动的 xml 简单接口。
要解析一份 xml 文档，而且在解析的过程中当某些事件发生时执行你希望此时执行的代码，就先准备以下三件事情。
l 获取一个 xml 解析器：到 xml.apache.org 免费获取。
l 获取 sax 类：上述的 xerces 解析器已经包括了，记得在 classpath 里包括他们。
l 获取一个 xml 文档：相信这个你自己可以搞定
接下来的事情，我认为以下的代码基本上说明了流程，其中要稍微解释的是 ContentHandler 接口。 SAX 2.0 定义了四个核心的处理接口，分别是 ContentHandler ， ErrorHandler ， DTDHandler ， EntityResolver 。其中较常用到的是前面两个，最后一个是处理 xml 里的实体的，而在 schema 较流行的今天， DTDHandler 也许不太需要注意。这些处理器可以被 set 到 parser 上，当 parser 在解析 xml 文档的过程中，发生特定的事件时，处理器中对应的方法便会被调用，当然了，方法的内容由你来写。这个基本上就是 sax 的概要情况了。
在读完代码和自己运行过下面的代码后，我相信你对 sax 的工作方式已经了解了，剩下的事情就是自己去熟悉另外几个处理器的方法。希望这篇东西能让你快速了解 sax ，而还有不少的细节，还需要自己去慢慢探讨了。
// 要实例化的reader的类名
private String vendroParserClass = " org.apache.xerces.parsers.SAXParser " ;
// 被读取的xml文件路径，以bin为根目录。
private String uri = " xmlDocuments/xmlPractise.xml " ;
// 为0时debugPrint方法不会打印数据。
private final int debug = 1 ;
public void test() throws IOException, SAXException {
XMLReader reader = null ;
try {
// 工厂方法以类名获得reader实例
reader = XMLReaderFactory.createXMLReader(vendroParserClass);
} catch (Exception e) {
e.printStackTrace();
}
// 以uri获取xml文档实例，reader.parse()方法可以接受一个
// 简单的uri作为参数，但是InputSource会更好。
InputSource inputSource = new InputSource(uri);
// 设置contentHandler
reader.setContentHandler( new MyContentHandler());
// 执行读取
reader.parse(inputSource);
System.out.println( " test completed. " );
}
public void debugPrint(String msg) {
if (debug > 0 ) {
System.out.print(msg);
}
}
// 内容处理器
class MyContentHandler implements ContentHandler {
// locator是定位器，指示当前解析文档进行到哪个位置了。
// 它只在解析生命周期内有效，解析完毕就别再碰它咯～
private Locator locator;
// 这个方法在整个解析过程的一开始被调用
public void setDocumentLocator(Locator locator) {
debugPrint( " setDocumentLocator get called.\n " );
this .locator = locator;
}
// xml文档开始时被调用
public void startDocument() throws SAXException {
debugPrint( " startDocument() get called.\n " );
}
// xml文档结束时被调用
public void endDocument() throws SAXException {
debugPrint( " endDocument() get called.\n " );
}
// xml文档的某个名称空间开始时被调用
public void startPrefixMapping(String prefix, String uri)
throws SAXException {
debugPrint( " start of : uri: " + uri + " , prefix: " + prefix + " .\n " );
}
// xml文档的某个名称空间结束时被调用
public void endPrefixMapping(String prefix) throws SAXException {
debugPrint( " end of: uri: " + uri + " , prefix: " + prefix + " .\n " );
}
// xml文档的某个元素开始时被调用
// uri是名称空间，localName是不带前缀的元素名，qName是前缀＋元素名
// atts就是属性列表了。
public void startElement(String uri, String localName, String qName,
Attributes atts) throws SAXException {
debugPrint( " < " + localName + " > " );
}
// xml文档的某个元素结束时被调用
public void endElement(String uri, String localName, String qName)
throws SAXException {
debugPrint( " </ " + localName + " > " );
}
// xml文档的某个元素的文本内容出现时被调用
// start和length是字符串截取的开始位置和长度，如下所示是比较好的
// 处理方法，先转换成String再处理
public void characters( char [] ch, int start, int length)
throws SAXException {
String s = new String(ch, start, length);
debugPrint(s);
}
// 遇到可以忽略的空白时被调用，关于xml里的空白，可以长篇大论，
// 这里就不废话了。
public void ignorableWhitespace( char [] ch, int start, int length)
throws SAXException {
// TODO Auto-generated method stub
}
// 遇到xml的处理指令时被调用
public void processingInstruction(String target, String data)
throws SAXException {
debugPrint( " PI target: ' " + target + " ', data: ' " + data + " '. " );
}
// 当xml里的实体被非验证解析器忽略时被调用
public void skippedEntity(String name) throws SAXException {
// TODO Auto-generated method stub
}
}
public static void main(String[] args) throws IOException, SAXException {
new Practice1().test();
}
}
题外话：以自己的学习的经历，感觉接触一门新技术的时候，详尽的经典著作未必最合适，如果要追求平缓的学习曲线，最好的方法是听学过的人谈谈整体的概念，看看运作实例，此时心中有了感性认识，再投入真正的学习中去，效果相当好。这也是写这篇东西的初衷了。文章很简陋，望勿见笑。
SAX is a event-driven simple api for xml.
There are three things to get before using SAX to parse a xml document, and make some code to execute when certain events comes up.
l Get an xml parser: download it from xml.apache.org for free.
l Get a SAX class: it should be included in the parser we mentioned above.
l Get an xml document: get the white mouse yourself.
The following is quite self-explanative, the codes describe the basic flow. Only the ContentHandler interface needs a little bit words. SAX 2.0 defined 4 core handler interfaces: ContentHandler, ErrorHandler, DTDHandler, EntityResolver. The leading 2 are often used, the last one is for the entity in xml, while schema is more prefer now, DTDHandler needs not much attention. These handlers can be set to a parser, when the parser is parsing the xml file, some certain events take places, the corresponding methods will be called back. The content in these methods, of course, will be finished by you, that’s what call-back is. Then it is the brief of SAX.
After reading and running the following codes, I believed that you are clear about how SAX works, what’s left is that you shall get familiar with other handlers. I hope this stuff can help you understand SAX in a short time, the details are left to yourself.
// name of the reader class that will be initialled.
private String vendroParserClass = " org.apache.xerces.parsers.SAXParser " ;
// file path of the xml file，using bin as file root 。
private String uri = " xmlDocuments/xmlPractise.xml " ;
// when this equasl 0, debugPrint() method won’t print message out。
private final int debug = 1 ;
public void test() throws IOException, SAXException {
XMLReader reader = null ;
try {
// using factory pattern
reader = XMLReaderFactory.createXMLReader(vendroParserClass);
} catch (Exception e) {
e.printStackTrace();
}
// get a xml file instance using uri，reader.parse()method can accept a simple
// uri as a parameter, but InputSource is better。
InputSource inputSource = new InputSource(uri);
// set the contentHandler
reader.setContentHandler( new MyContentHandler());
// executing the parsing
reader.parse(inputSource);
System.out.println( " test completed. " );
}
public void debugPrint(String msg) {
if (debug > 0 ) {
System.out.print(msg);
}
}
// content handler
class MyContentHandler implements ContentHandler {
// locator indicate the current position when parsing the file
// it is only valid during parsing, so don’t touch it after the parsing is finished
private Locator locator;
// this method will be the first method called as the parsing begins.
public void setDocumentLocator(Locator locator) {
debugPrint( " setDocumentLocator get called.\n " );
this .locator = locator;
}
// this method will be called at the start of a xml file
public void startDocument() throws SAXException {
debugPrint( " startDocument() get called.\n " );
}
// this method will be called at the end of a xml file
public void endDocument() throws SAXException {
debugPrint( " endDocument() get called.\n " );
}
// this method will be called at the start of a namespace
public void startPrefixMapping(String prefix, String uri)
throws SAXException {
debugPrint( " start of : uri: " + uri + " , prefix: " + prefix + " .\n " );
}
// this method will be called at the end of a namespace
public void endPrefixMapping(String prefix) throws SAXException {
debugPrint( " end of: uri: " + uri + " , prefix: " + prefix + " .\n " );
}
// this method will be called at the start of an element
public void startElement(String uri, String localName, String qName,
Attributes atts) throws SAXException {
debugPrint( " < " + localName + " > " );
}
// this method will be called at the end of an element
public void endElement(String uri, String localName, String qName)
throws SAXException {
debugPrint( " </ " + localName + " > " );
}
// x this method will be called when the text content appears
// start and length is the start index and length of the char array.
// parsed to a String before handling the content will be a good choice
public void characters( char [] ch, int start, int length)
throws SAXException {
String s = new String(ch, start, length);
debugPrint(s);
}
// this method will be called when some ignorable white space appears,
// there are much to talk about white space in xml, we aren’t talking them here.
public void ignorableWhitespace( char [] ch, int start, int length)
throws SAXException {
// TODO Auto-generated method stub
}
// this method will be called when processing instructions appears
public void processingInstruction(String target, String data)
throws SAXException {
debugPrint( " PI target: ' " + target + " ', data: ' " + data + " '. " );
}
// this method will be called when the entity in the xml file is skipped by the // parser.
public void skippedEntity(String name) throws SAXException {
// TODO Auto-generated method stub
}
}
public static void main(String[] args) throws IOException, SAXException {
new Practice1().test();
}
}