日常小结-SAX解析xml

SAX可用在解析的过程中处理xml而不需要等到整个文件都存入内存在进行解析：

SAX解析

SAX采用事件处理的方式解析XML文件，利用SAX解析XML文件，涉及两个部分，解析器和事件处理器。

解析器可用使用JAXP的API创建，创建出SAX解析器后，就可以指定解析器去解析某个xml文档。

解析器采用sax方式在解析某个xml文档时，它只要解析到xml文档的一个组成部分，都会调用事件处理器的一个方法，解析器在调用事件处理器的方法时，会把当前解析到的xml文件内容作为方法的参数传递给事件处理器。

事件处理器由程序员编写，程序员通过事件处理器中方法的参数，就可以很轻松的得到sax解析器解析到的数据，从而决定对数据进行处理



阅读ContentHandler API文档，常用方法：

- startElement

- endElement

- characters

例子：

<?xml version="1.0" encoding="UTF-8"?>
<书架>
<书>
<书名 name="xxxxx">java教程</书名>
<作者>张孝祥</作者>
<售价>109元</售价>
<售价>39.00元</售价>
</书>
<书>
<书名>javaScript教程</书名>
<作者>张孝祥</作者>
<售价>28元</售价>
</书>
</书架>

下面程序用于提取所有标签：

package demo;

import java.io.IOException;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;

import javax.xml.parsers.SAXParserFactory;

import jdk.internal.org.xml.sax.Attributes;
import jdk.internal.org.xml.sax.ContentHandler;
import jdk.internal.org.xml.sax.Locator;

import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;

public class Demo1 {

/*
* sax 解析xml文档
*/

public static void main(String [] args) throws ParserConfigurationException, SAXException, IOException{
//1.创建解析工厂（抽象工厂）
SAXParserFactory factory = SAXParserFactory.newInstance();

//2.得到解析器
SAXParser sp = factory.newSAXParser();

//3.得到读取器
XMLReader reader = sp.getXMLReader();

//4.设置内容处理器
reader.setContentHandler(  new ListHandler());

//5.读取xml文档内容
reader.parse("src/book.xml");
}

}

//得到xml文档所有内容
class ListHandler implements  org.xml.sax.ContentHandler
{

public void characters(char[] arg0, int arg1, int arg2) {
// TODO Auto-generated method stub
System.out.println(new String(arg0,arg1,arg2));
}

public void endDocument() {
// TODO Auto-generated method stub

}

public void endElement(String arg0, String arg1, String arg2) {
// TODO Auto-generated method stub
System.out.println("<"+arg2+">");
}

public void endPrefixMapping(String arg0) {
// TODO Auto-generated method stub

}

public void ignorableWhitespace(char[] arg0, int arg1, int arg2) {
// TODO Auto-generated method stub

}

public void processingInstruction(String arg0, String arg1) {
// TODO Auto-generated method stub

}

public void setDocumentLocator(Locator arg0) {
// TODO Auto-generated method stub

}

public void skippedEntity(String arg0) {
// TODO Auto-generated method stub

}

public void startDocument() {
// TODO Auto-generated method stub

}

public void startElement(String arg0, String arg1, String arg2,
Attributes arg3) throws jdk.internal.org.xml.sax.SAXException {
// TODO Auto-generated method stub
System.out.println("<"+arg2+">");

for (int i = 0; arg3!=null && i < arg3.getLength(); i++) {
String attName = arg3.getQName(i);
String attValue = arg3.getValue(i);
System.out.println(attName+"="+attValue);

}
}

public void startPrefixMapping(String arg0, String arg1) {
// TODO Auto-generated method stub

}

public void setDocumentLocator(org.xml.sax.Locator locator) {
// TODO Auto-generated method stub

}

public void startElement(String uri, String localName, String qName,
org.xml.sax.Attributes atts) throws SAXException {
// TODO Auto-generated method stub

}

}

下列程序用于提取特定标签：

package demo;

import java.io.IOException;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;

public class Demo2 {

/*
* sax 解析xml文档
*/

public static void main(String [] args) throws ParserConfigurationException, SAXException, IOException{
//1.创建解析工厂（抽象工厂）
SAXParserFactory factory = SAXParserFactory.newInstance();

//2.得到解析器
SAXParser sp = factory.newSAXParser();

//3.得到读取器
XMLReader reader = sp.getXMLReader();

//4.设置内容处理器
reader.setContentHandler(  new TagValueHandler());

//5.读取xml文档内容
reader.parse("src/book.xml");
}

}

//或者指定标签的值
class TagValueHandler extends DefaultHandler{

private String currenTage;//当前解析到的标签
@Override
public void startElement(String uri, String localName, String qName,
Attributes attributes) throws SAXException {
// TODO Auto-generated method stub
currenTage = qName;

}

@Override
public void characters(char[] ch, int start, int length)
throws SAXException {
// TODO Auto-generated method stub
if("作者".equals(currenTage)){
System.out.println(new String(ch,start,length));
}
}

@Override
public void endElement(String uri, String localName, String qName)
throws SAXException {
// TODO Auto-generated method stub
currenTage = null;
}
}

下列代码用于将xml解析后封装到bean的list中：

package demo;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;

public class Demo3 {

/*
* sax 解析xml文档
*/

public static void main(String [] args) throws ParserConfigurationException, SAXException, IOException{
//1.创建解析工厂（抽象工厂）
SAXParserFactory factory = SAXParserFactory.newInstance();

//2.得到解析器
SAXParser sp = factory.newSAXParser();

//3.得到读取器
XMLReader reader = sp.getXMLReader();

//4.设置内容处理器
BeanListHandler handler = new BeanListHandler();
reader.setContentHandler( handler );

//5.读取xml文档内容
reader.parse("src/book.xml");
List list = handler.getBooks();
System.out.println(list);
}

}

class BeanListHandler extends DefaultHandler{

private List list = new ArrayList();
private String currentTag;
private Book book;

@Override
public void startElement(String uri, String localName, String qName,
Attributes attributes) throws SAXException {
// TODO Auto-generated method stub
currentTag = qName;
if("书".equals(currentTag)){
book = new Book();
}
}

@Override
public void characters(char[] ch, int start, int length)
throws SAXException {
// TODO Auto-generated method stub
if("书名".equals(currentTag)){
String name = new String(ch,start,length);
book.setName(name);
}
if("作者".equals(currentTag)){
String author = new String(ch,start,length);
book.setAuthor(author);
}
if("售价".equals(currentTag)){
String price = new String(ch,start,length);
book.setPrice(price);
}
}

@Override
public void endElement(String uri, String localName, String qName)
throws SAXException {
// TODO Auto-generated method stub
if("书".equals(qName)){
list.add(book);
book = null;
}
currentTag = null;
}

public List getBooks() {
return list;
}

}

下列代码用于提供bean类

package demo;

public class Book {
private String name;
private String author;
private String price;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public String getPrice() {
return price;
}
public void setPrice(String price) {
this.price = price;
}

}