XML SAX解析详解

DOM和SAX的最终作用是可以让我们利用java Javascript等语言来获取xml文件中的节点及文本、属性等信息。

本文引自其他博客，内容易懂，为了节省时间，直接摘抄过来了。 JAVA 解析 XML 通常有两种方式，DOM 和 SAX。DOM 虽然是 W3C 的标准，提供了标准的解析方式，但它的解析效率一直不尽如人意，因为使用DOM解析XML时，解析器读入整个文档并构建一个驻留内存的树结构（节点树），然后您的代码才可以使用 DOM 的标准接口来操作这个树结构。但大部分情况下我们只对文档的部分内容感兴趣，根本就不用先解析整个文档，并且从节点树的根节点来索引一些我们需要的数据也是非常耗时的。

SAX是一种XML解析的替代方法。相比于文档对象模型DOM，SAX 是读取和操作 XML 数据的更快速、更轻量的方

法。SAX 允许您在读取文档时处理它，从而不必等待整个文档被存储之后才采取操作。它不涉及 DOM 所必需的开销和概念跳跃。 SAX API是一个基于事件的API ，适用于处理数据流，即随着数据的流动而依次处理数据。SAX API

在其解析您的文档时发生一定事件的时候会通知您。在您对其响应时，您不作保存的数据将会被抛弃。

下面是一个SAX解析XML的示例（有点长，因为详细注解了SAX事件处理的所有方法），SAX API中主要有四种处理事件的接口，它们分别是ContentHandler，DTDHandler， EntityResolver 和 ErrorHandler 。下面的例子可能有点冗长，实际上只要继承DefaultHandler 类，再覆盖一部分处理事件的方法同样可以达到这个示例的效果，但为了纵观全局，还是看看SAX API里面所有主要的事件解析方法吧。（实际上DefaultHandler就是实现了上面的四个事件处理器接口，然后提供了每个抽象方法的默认实现。）

1，ContentHandler 接口：接收文档逻辑内容的通知的处理器接口。

Java代码收藏代码

'import org.xml.sax.Attributes;

import org.xml.sax.ContentHandler;

import org.xml.sax.Locator;

import org.xml.sax.SAXException;

class MyContentHandler implements ContentHandler{

StringBuffer jsonStringBuffer ;

int frontBlankCount = 0;

public MyContentHandler(){

jsonStringBuffer = new StringBuffer();

}

@Override

public void characters(char[] ch, int begin, int length) throws SAXException {

StringBuffer buffer = new StringBuffer();

for(int i = begin ; i < begin+length ; i++){

switch(ch[i]){

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\");break;

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\r':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\r");break;

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n");break;

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t");break;

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"");break;

default : buffer.append(ch[i]);

}

System.out.println(this.toBlankString(this.frontBlankCount)+

">>> characters("+length+"): "+buffer.toString());

}

@Override

public void enddocument() throws SAXException {

System.out.println(this.toBlankString(--this.frontBlankCount)+

">>> end document");

}

@Override

public void endElement(String uri,String localName,String qName)

throws SAXException {

System.out.println(this.toBlankString(--this.frontBlankCount)+

">>> end element : "+qName+"("+uri+")");

}

@Override

public void endPrefixMapping(String prefix) throws SAXException {

System.out.println(this.toBlankString(--this.frontBlankCount)+

">>> end prefix_mapping : "+prefix);

}

@Override

public void ignorableWhitespace(char[] ch, int begin, int length)

throws SAXException {

StringBuffer buffer = new StringBuffer();

for(int i = begin ; i < begin+length ; i++){

switch(ch[i]){

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\r':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\r");break;

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n");break;

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t");break;

case '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"':buffer.append("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"");break;

default : buffer.append(ch[i]);

}

System.out.println(this.toBlankString(this.frontBlankCount)+">>> ignorable whitespace("+length+"): "+buffer.toString());

}

@Override

public void processingInstruction(String target,String data)

throws SAXException {

System.out.println(this.toBlankString(this.frontBlankCount)+">>> process instruction : (target = \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\""

+target+"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\",data = \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\""+data+"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\")");

}

@Override

public void setdocumentLocator(Locator locator) {

System.out.println(this.toBlankString(this.frontBlankCount)+

">>> set document_locator : (lineNumber = "+locator.getLineNumber()

+",columnNumber = "+locator.getColumnNumber()

+",systemId = "+locator.getSystemId()

+",publicId = "+locator.getPublicId()+")");

}

@Override

public void skippedEntity(String name) throws SAXException {

System.out.println(this.toBlankString(this.frontBlankCount)+

">>> skipped_entity : "+name);

}

@Override

public void startdocument() throws SAXException {

System.out.println(this.toBlankString(this.frontBlankCount++)+

">>> start document ");

}

@Override

public void startElement(String uri, String localName, String qName,

Attributes atts) throws SAXException {

System.out.println(this.toBlankString(this.frontBlankCount++)+

">>> start element : "+qName+"("+uri+")");

}

@Override

public void startPrefixMapping(String prefix,String uri)

throws SAXException {

System.out.println(this.toBlankString(this.frontBlankCount++)+

">>> start prefix_mapping : xmlns:"+prefix+" = "

+"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\""+uri+"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"");

}

private String toBlankString(int count){

StringBuffer buffer = new StringBuffer();

for(int i = 0;i

buffer.append(" ");

return buffer.toString();

}

2，DTDHandler 接口：接收与 DTD 相关的事件的通知的处理器接口。

Java代码收藏代码

'import org.xml.sax.DTDHandler;

import org.xml.sax.SAXException;

public class MyDTDHandler implements DTDHandler {

@Override

public void notationDecl(String name, String publicId, String systemId)

throws SAXException {

System.out.println(">>> notation declare : (name = "+name

+",systemId = "+publicId

+",publicId = "+systemId+")");

}

@Override

public void unparsedEntityDecl(String name,

String publicId,

String systemId,

String notationName) throws SAXException {

System.out.println(">>> unparsed entity declare : (name = "+name

+",systemId = "+publicId

+",publicId = "+systemId

+",notationName = "+notationName+")");

}

3，EntityResolver 接口：是用于解析实体的基本接口。

Java代码收藏代码

'import java.io.IOException;

import org.xml.sax.EntityResolver;

import org.xml.sax.InputSource;

import org.xml.sax.SAXException;

public class MyEntityResolver implements EntityResolver {

@Override

public InputSource resolveEntity(String publicId, String systemId)

throws SAXException, IOException {

return null;

}

4，ErrorHandler接口：是错误处理程序的基本接口。

Java代码收藏代码

import org.xml.sax.ErrorHandler;

import org.xml.sax.SAXException;

import org.xml.sax.SAXParseException;

public class MyErrorHandler implements ErrorHandler {

@Override

public void error(SAXParseException e) throws SAXException {

System.err.println("Error ("+e.getLineNumber()+","

+e.getColumnNumber()+") : "+e.getMessage());

}

@Override

public void fatalError(SAXParseException e) throws SAXException {

System.err.println("FatalError ("+e.getLineNumber()+","

+e.getColumnNumber()+") : "+e.getMessage());

}

@Override

public void warning(SAXParseException e) throws SAXException {

System.err.println("Warning ("+e.getLineNumber()+","

+e.getColumnNumber()+") : "+e.getMessage());

}

Test 类的主方法打印解析books.xml时的事件信息。

Java代码收藏代码

import java.io.FileNotFoundException;

import java.io.FileReader;

import java.io.IOException;

import org.xml.sax.ContentHandler;

import org.xml.sax.DTDHandler;

import org.xml.sax.EntityResolver;

import org.xml.sax.ErrorHandler;

import org.xml.sax.InputSource;

import org.xml.sax.SAXException;

import org.xml.sax.XMLReader;

import org.xml.sax.helpers.XMLReaderFactory;

public class Test {

public static void main(String[] args) throws SAXException,

FileNotFoundException, IOException {

//创建处理文档内容相关事件的处理器

ContentHandler contentHandler = new MyContentHandler();

//创建处理错误事件处理器

ErrorHandler errorHandler = new MyErrorHandler();

//创建处理DTD相关事件的处理器

DTDHandler dtdHandler = new MyDTDHandler();

//创建实体解析器

EntityResolver entityResolver = new MyEntityResolver();

//创建一个XML解析器（通过SAX方式读取解析XML）

XMLReader reader = XMLReaderFactory.createXMLReader();

reader.setFeature("http://xml.org/sax/features/validation",true);

reader.setFeature("http://xml.org/sax/features/namespaces",true);

//设置XML解析器的处理文档内容相关事件的处理器

reader.setContentHandler(contentHandler);

//设置XML解析器的处理错误事件处理器

reader.setErrorHandler(errorHandler);

//设置XML解析器的处理DTD相关事件的处理器

reader.setDTDHandler(dtdHandler);

//设置XML解析器的实体解析器

reader.setEntityResolver(entityResolver);

//解析books.xml文档

reader.parse(new InputSource(new FileReader("books.xml")));

}

books.xml 文件的内容如下：

Xml代码收藏代码

Thinking in JAVA

Core JAVA2

C++ primer

控制台输出如下：

>>> set document_locator : (lineNumber = 1,columnNumber = 1,systemId = null,publicId = null)

>>> start document

Error (2,7) : document is invalid: no grammar found.

Error (2,7) : document root element "books", must match DOCTYPE root "null".

>>> start prefix_mapping : xmlns: = "http://test.org/books"

>>> start element : books(http://test.org/books)