XML SAX解析详解

编辑: admin 分类: html 发布时间: 2022-06-06 来源:互联网

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();

}

/*

* 接收字符数据的通知。

* 在DOM中 ch[begin:end] 相当于Text节点的节点值(nodeValue)

*/

@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());

}



/*

* 接收文档的结尾的通知。

*/

@Override

public void endDocument() throws SAXException {

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

">>> end document");

}



/*

* 接收文档的结尾的通知。

* 参数意义如下:

* uri :元素的命名空间

* localName :元素的本地名称(不带前缀)

* qName :元素的限定名(带前缀)

*

*/

@Override

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

throws SAXException {

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

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

}


/*

* 结束前缀 URI 范围的映射。

*/

@Override

public void endPrefixMapping(String prefix) throws SAXException {

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

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

}


/*

* 接收元素内容中可忽略的空白的通知。

* 参数意义如下:

* ch : 来自 XML 文档的字符

* start : 数组中的开始位置

* length : 从数组中读取的字符的个数

*/

@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 '\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\':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)+">>> ignorable whitespace("+length+"): "+buffer.toString());

}


/*

* 接收处理指令的通知。

* 参数意义如下:

* target : 处理指令目标

* data : 处理指令数据,如果未提供,则为 null。

*/

@Override

public void processingInstruction(String target,String data)

throws SAXException {

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

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

}


/*

* 接收用来查找 SAX 文档事件起源的对象。

* 参数意义如下:

* locator : 可以返回任何 SAX 文档事件位置的对象

*/

@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()+")");


}


/*

* 接收跳过的实体的通知。

* 参数意义如下:

* name : 所跳过的实体的名称。如果它是参数实体,则名称将以 '%' 开头,

* 如果它是外部 DTD 子集,则将是字符串 "[dtd]"

*/

@Override

public void skippedEntity(String name) throws SAXException {

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

">>> skipped_entity : "+name);

}


/*

* 接收文档的开始的通知。

*/

@Override

public void startDocument() throws SAXException {

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

">>> start document ");

}


/*

* 接收元素开始的通知。

* 参数意义如下:

* uri :元素的命名空间

* localName :元素的本地名称(不带前缀)

* qName :元素的限定名(带前缀)

* atts :元素的属性集合

*/

@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+")");

}


/*

* 开始前缀 URI 名称空间范围映射。

* 此事件的信息对于常规的命名空间处理并非必需:

* 当 http://xml.org/sax/features/namespaces 功能为 true(默认)时,

* SAX XML 读取器将自动替换元素和属性名称的前缀。

* 参数意义如下:

* prefix :前缀

* uri :命名空间

*/

@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 {


/*

* 接收注释声明事件的通知。

* 参数意义如下:

* name - 注释名称。

* publicId - 注释的公共标识符,如果未提供,则为 null。

* systemId - 注释的系统标识符,如果未提供,则为 null。

*/

@Override

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

throws SAXException {

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

+",systemId = "+publicId

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

}


/*

* 接收未解析的实体声明事件的通知。

* 参数意义如下:

* name - 未解析的实体的名称。

* publicId - 实体的公共标识符,如果未提供,则为 null。

* systemId - 实体的系统标识符。

* notationName - 相关注释的名称。

*/

@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 {


/*

* 允许应用程序解析外部实体。

* 解析器将在打开任何外部实体(顶级文档实体除外)前调用此方法

* 参数意义如下:

* publicId : 被引用的外部实体的公共标识符,如果未提供,则为 null。

* systemId : 被引用的外部实体的系统标识符。

* 返回:

* 一个描述新输入源的 InputSource 对象,或者返回 null,

* 以请求解析器打开到系统标识符的常规 URI 连接。

*/

@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 {


/*

* 接收可恢复的错误的通知

*/

@Override

public void error(SAXParseException e) throws SAXException {

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

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

}


/*

* 接收不可恢复的错误的通知。

*/

@Override

public void fatalError(SAXParseException e) throws SAXException {

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

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

}


/*

* 接收不可恢复的错误的通知。

*/

@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();

/*

* 设置解析器的相关特性

* http://xml.org/sax/features/validation = true 表示开启验证特性

* http://xml.org/sax/features/namespaces = true 表示开启命名空间特性

*/

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)

>>> characters(2): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

>>> characters(2): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

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

>>> characters(3): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

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

>>> characters(16): Thinking in JAVA

>>> end element : name(http://test.org/books)

>>> characters(2): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

>>> end element : book(http://test.org/books)

>>> characters(2): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

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

>>> characters(3): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

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

>>> characters(10): Core JAVA2

>>> end element : name(http://test.org/books)

>>> characters(2): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

>>> end element : book(http://test.org/books)

>>> characters(2): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

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

>>> characters(3): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

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

>>> characters(10): C++ primer

>>> end element : name(http://test.org/books)

>>> characters(2): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\t

>>> end element : book(http://test.org/books)

>>> characters(1): \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n

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

>>> end prefix_mapping :

>>> end document

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