xml_SAX解析

（一）SAX解析

  

1.1 SAX解析
SAX：基于事件处理的机制
sax解析xml文件时，遇到根开始标签，根结束标签，开始解析文件，文件解析结束，字符内容，空白字符等都会触发各自的方法。

优点：
适合解析大文件，对内存要求不高
轻量级的解析数据方式，效率更高
缺点：
不能随机解析(只能从头开始解析，一点点往后进行)
不能修改XML文件，只能进行查询

1.2用SAX解析遍历整个xml文件并进行原样输出

1.2.1 java代码

package xml4;

import java.io.File;
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.helpers.DefaultHandler;

public class SaxTest {
	public static void main(String[] args) {
		// SAX解析 ①获取factory工厂
		SAXParserFactory factory = SAXParserFactory.newInstance();

		try {
			// SAX ②获取解析器
			SAXParser parser = factory.newSAXParser();
			// 获取handel的对象
			SaxTestHandel sh = new SaxTestHandel();
			try {
				parser.parse(new File("src/xml4/desk.xml"), sh);
			} catch (IOException e) {
				e.printStackTrace();
			}

		} catch (ParserConfigurationException e) {
			e.printStackTrace();
		} catch (SAXException e) {
			e.printStackTrace();
		}

	}
}

class SaxTestHandel extends DefaultHandler {
	//当开始读到这个文件时，触发该相应
	@Override
	public void startDocument() throws SAXException {
		System.out.println("开始解析了！");
	}
	//读完了，所有的，触发该方法
	@Override
	public void endDocument() throws SAXException {
		//System.out.println("解析完了！");
	}
	
	//读到元素标签时，触发该方法
	@Override
	public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
		System.out.print("<");
		System.out.print(qName);
		for(int i=0;i<attributes.getLength();i++) {
			String qName2 = attributes.getQName(i);
			String value = attributes.getValue(qName2);
			System.out.print(" "+qName2+"="+"'"+value+"'");
		}
		System.out.print(">");
	}
	
	@Override
	public void endElement(String uri, String localName, String qName) throws SAXException {
		System.out.print("</"+qName+">");
	}

	@Override
	public void characters(char[] ch, int start, int length) throws SAXException {
			String str=new String(ch,start,length);
			System.out.print(str);
	}

}

1.2.2 Xml代码

<?xml version="1.0" encoding="UTF-8"?>
<disks>
	<disk name='c盘'>
		<size>10G</size>
		<directory>100</directory>
		<file>200</file>
	</disk>

	<disk name='d盘'>
		<size>20G</size>
		<directory>200</directory>
		<file>3000</file>
	</disk>
</disks>

 1.3  小练习 题目：获取一个xml 文件中的信息，并把它封装到一个实体类中去，并存放到一个集合中去，并保存到本地文件中去 

package xml4;

public class Disk {
    
    private String name;
    private String size;
    private String directory;
    private int  file;
    public Disk(String name, String size, String directory, int file) {
        super();
        this.name = name;
        this.size = size;
        this.directory = directory;
        this.file = file;
    }
    public Disk() {
        super();
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSize() {
        return size;
    }
    public void setSize(String size) {
        this.size = size;
    }
    public String getDirectory() {
        return directory;
    }
    public void setDirectory(String directory) {
        this.directory = directory;
    }
    public int getFile() {
        return file;
    }
    public void setFile(int file) {
        this.file = file;
    }
    @Override
    public String toString() {
        return "Disk [name=" + name + ", size=" + size + ", directory=" + directory + ", file=" + file + "]";
    }
    
}

package xml4;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;

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.helpers.DefaultHandler;

import sun.awt.FwDispatcher;

public class SaxTest2 {
	public static void main(String[] args) {
		SAXParserFactory factory = SAXParserFactory.newInstance();
		try {
			File f = new File("src/xml4/desk.xml");
			SaxTest2Hander dh = new SaxTest2Hander();
			SAXParser parser = factory.newSAXParser();
			
			try {
				parser.parse(f, dh);
			} catch (IOException e) {
				e.printStackTrace();
			}
		} catch (ParserConfigurationException e) {
			e.printStackTrace();
		} catch (SAXException e) {
			e.printStackTrace();
		}
	}
}

class SaxTest2Hander extends DefaultHandler {
	private ArrayList<Disk> list;
	private Disk disk;
	private String tagName;
	

	@Override
	public void startDocument() throws SAXException {
		list=new ArrayList<Disk>();
	}

	@Override
	public void endDocument() throws SAXException {
		
		try {
			PrintWriter fw=new PrintWriter("src/xml4/desk.txt");
			for (Disk disk : list) {
				fw.println(disk);
				fw.flush();
			}
			fw.close();
			
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	@Override
	public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
			if("disk".equals(qName)) {
				disk=new Disk();
			}else {
				tagName=qName;
			}
			for(int i=0;i<attributes.getLength();i++) {
					String qName2 = attributes.getQName(0);
					String value = attributes.getValue(qName2);
					if(qName2.equals("name")){
						disk.setName(value);
					}					
			}
	}

	@Override
	public void endElement(String uri, String localName, String qName) throws SAXException {
			if("disk".equals(qName)) {
				list.add(disk);
			}else {
				tagName=null;
			}
		
	}

	@Override
	public void characters(char[] ch, int start, int length) throws SAXException {
		String str=new String(ch,start,length);
		if("size".equals(tagName)) {
			disk.setSize(str);
		}
		if("directory".equals(tagName)) {
			disk.setDirectory(str);
		}
		if("file".equals(tagName)) {
			disk.setFile(Integer.parseInt(str));
		}
	}

}

　　

<?xml version="1.0" encoding="UTF-8"?>
<disks>
	<disk name='c盘'>
		<size>10G</size>
		<directory>100</directory>
		<file>200</file>
	</disk>

	<disk name='d盘'>
		<size>20G</size>
		<directory>200</directory>
		<file>3000</file>
	</disk>
</disks>