数据存储（二）--SAX引擎XML存储（附Demo）

Android SDK支持采用SAX技术读取XML,SAX采用顺序读取的方式来处理XML文档。这就要求在每读取XML文档的某个节点时会触发相应的事件来处理这个节点。下面基于一个实例讲述SAX的使用：

public class Book 
{
	private String name;
	private String id;
	private String price;
	private String publisher;
	private int count;
    .... get,set方法省略
}

XML文件如下：

<?xml version="1.0" encoding="utf-8"?>
<books  xmlns:book="http://schemas.android.com/com.example.jsonxmlio">   
    <book 
        book:name="语文"
        book:id="001" 
       	book:price="45"
       	book:publisher="A">12</book>
    <book 
        book:name="数学"
        book:id="002" 
       	book:price="50"
       	book:publisher="B">10</book>
    <book 
        book:name="英语"
        book:id="003" 
       	book:price="55"
       	book:publisher="C">21</book> 
</books>

XMLTool.java

1.构建一个工厂SAXParserFactory
2.构建并实例化SAXPraser对象

public class XMLTool {
	
	private static SAXParser getSAXParser() throws ParserConfigurationException,SAXException
	{
        SAXParserFactory parserFactory = SAXParserFactory.newInstance();
        return parserFactory.newSAXParser();
	}
	public static DefaultHandler parse(InputStream inStream,DefaultHandler handler){
		if(inStream!=null){
			try {
				SAXParser parser = getSAXParser();
				parser.parse(inStream,handler);
				return handler;
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}finally{
				if(inStream!=null){
					try {
						inStream.close();
					} catch (IOException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
				}
			}
		}
		return null;
	}
}

BookXMLParser.java

public class BookXMLParser extends DefaultHandler
{
	
	private ArrayList<Book> dataList;
	private Book book;
	private StringBuffer stringBuffer = new StringBuffer();
	//private StringBuffer buffer=new StringBuffer();
	
	public ArrayList<Book> getData()
	{
		return dataList;
	}
	
	public void startDocument() throws SAXException 
	{
		// TODO Auto-generated method stub
		dataList = new ArrayList<Book>();
	}
	
	public void startElement(String uri,String localName,String qName,Attributes attributes) throws SAXException 
	{
		// TODO Auto-generated method stub
		if(qName.equals("book"))
		{
			book = new Book();
			book.setName(attributes.getValue("book:name"));
			book.setId(attributes.getValue("book:id"));
			book.setPrice(attributes.getValue("book:price"));
			book.setPublisher(attributes.getValue("book:publisher"));
			
		}
		super.startElement(uri,localName,qName,attributes);
	}

	@Override
	public void characters(char[] ch,int start,int length)
			throws SAXException {
		// TODO Auto-generated method stub
		stringBuffer.append(ch,start,length);
		super.characters(ch,length);
	}

	@Override
	public void endElement(String uri,String qName)
			throws SAXException {
		// TODO Auto-generated method stub
		if(qName.equals("book"))
		{
			if(stringBuffer.toString()!=null && !stringBuffer.toString().equals(""))
			{
				book.setCount(Integer.parseInt(stringBuffer.toString().trim()));
				stringBuffer.setLength(0);//必须清空缓冲区
			}
			dataList.add(book);
			
		}
		super.endElement(uri,qName);
	}
}

1.开始分析XML文件。该分析点表示SAX引擎刚刚开始处理XML文件，但是还没有读取XML文件中的内容，该分析点对应：

public void startDocument() throws SAXException 
	{
		// TODO Auto-generated method stub
		dataList = new ArrayList<Book>();
	}

2.开始处理每一个XML元素。也就是遇到<book>这样的起始标记的时候都会触发这个分析节点，所对应的事件方法是startElement。在这个节点可以获得元素的名称、属性的相关信息。

public void startElement(String uri,Attributes attributes) throws SAXException 
	{
		// TODO Auto-generated method stub
		if(qName.equals("book"))
		{
			book = new Book();
			book.setName(attributes.getValue("book:name"));
			book.setId(attributes.getValue("book:id"));
			book.setPrice(attributes.getValue("book:price"));
			book.setPublisher(attributes.getValue("book:publisher"));
		}
		super.startElement(uri,attributes);
	}

	public void endElement(String uri,String qName)
			throws SAXException {
		// TODO Auto-generated method stub
		if(qName.equals("book"))
		{
			if(stringBuffer.toString()!=null && !stringBuffer.toString().equals(""))
			{
				book.setCount(Integer.parseInt(stringBuffer.toString().trim()));
				stringBuffer.setLength(0);//必须清空缓冲区
			}
			dataList.add(book);
		}
		super.endElement(uri,qName);
	}

5.读取字符分析点。这是一个很重要的分析点。如果没有这个分析点， 前面的工作相当于白做，虽然扫描了XML文件，但是没有保存.....而这个分析点所对应的characters事件方法的主要作用就是保存SAX读取的XML文件内容。具体的说就是<book ... ...>12</book>中的“12”

public void characters(char[] ch,length);
	}

使用SAX解析XML:

public class MainActivity extends Activity 
{
	private List<Book> books;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		InputStream inStream = getResources().openRawResource(R.raw.books);
		BookXMLParser parser = new BookXMLParser();
		books = ((BookXMLParser)XMLTool.parse(inStream,parser)).getData();
		
		if(books!=null && books.size()>0)
		{
			for(int i = 0;i<books.size();i++)
			{
				Log.d("AAA",books.get(i).toString());
			}
		}
	}
}

写XML文件

public static void WriteXML(List<Book> books,OutputStream out) throws Exception 
	{
        XmlSerializer serializer = Xml.newSerializer();
        serializer.setOutput(out,"UTF-8");
        serializer.startDocument("UTF-8",true);
        serializer.startTag(null,"books");        
        for (Book book : books) 
        {
            serializer.startTag(null,"book");            
            serializer.attribute(null,"book:name",book.getName());            
            serializer.attribute(null,"book:id",book.getId()); 
            serializer.attribute(null,"book:price",book.getPrice());            
            serializer.attribute(null,"book:publisher",book.getPublisher());          
            serializer.text(String.valueOf(book.getCount()));            
            serializer.endTag(null,"book");
        }        
        serializer.endTag(null,"books");
        serializer.endDocument();
        out.flush();
        out.close();
    }

（编辑：李大同）

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