XML的JAVA 解析（一）(6a)

下列代码说明这种ContentHandler轮换技术。Contents缓存被类Example6和其它特定ContentHandler内部类共享：

import org.xml.sax.*;
import org.xml.sax.helpers.*;
import java.io.*;
import java.util.*;
import common.*;

public class Example6 extends DefaultHandler {

   // XML解析．．．
   XMLReader parser;

        // 被解析对象．．．
        Example6Circle circleMapper = new Example6Circle();
        Example6Square squareMapper = new Example6Square();
        Example6Triangle triangleMapper = new Example6Triangle();

  // 不同形体的本地向量表．．．
   private Vector circles = new Vector();
   private Vector triangles = new Vector();
   private Vector squares = new Vector();

  // 从"characters" SAX事件中收集数据的缓存。
   private CharArrayWriter contents = new CharArrayWriter();

   // 用XML解析器为参数的构造函数．．．
   Example6( XMLReader parser ) {
           this.parser = parser;
   }

  // 重载DefaultHandler类以拦截SAX事件的方法。
   //
        // 头于所有有效事件的详细内容，参见org.xml.sax.ContentHandler。
   //
   public void startElement( String namespaceURI,
               String localName,
              String qName,
              Attributes attr ) throws SAXException {

      contents.reset();

      if ( localName.equals( "Circle" ) ) {
                        Circle aCircle = new Circle();
         aCircle.name = attr.getValue( "name" );
         circles.addElement( aCircle );
         circleMapper.collectCircle( parser, this, aCircle );
      }

      if ( localName.equals( "Square" ) ) {
                    Square aSquare = new Square();
         aSquare.name = attr.getValue( "name" );
         squares.addElement( aSquare );
         squareMapper.collectSquare( parser, this, aSquare );
      }

      if ( localName.equals( "Triangle" ) ) {
         Triangle aTriangle = new Triangle();
         aTriangle.name = attr.getValue( "name" );
         triangles.addElement( aTriangle );
         triangleMapper.collectTriangle( parser, this, aTriangle);
      }
   }

   public void endElement( String namespaceURI,
               String localName,
              String qName ) throws SAXException {

      // endElement SAX事件中已经没有需要Example 6映射器处理的了。
      
   }

   public void characters( char[] ch, int start, int length )
                  throws SAXException {
      // // 将数据内容写入缓存。
      contents.write( ch, start, length );

   }

   public Vector getCircles() {
           return circles;
   }

   public Vector getSquares() {
           return squares;
   }

   public Vector getTriangles() {
           return triangles;
   }

   public static void main( String[] argv ){

      System.out.println( "Example6:" );
      try {

        // 创建SAX 2解析器．．．
         XMLReader xr = XMLReaderFactory.createXMLReader();

        // 安装ContentHandler．．．
         Example6 ex6 = new Example6(xr);
         xr.setContentHandler( ex6 );

        // 解析文件．．．
         xr.parse( new InputSource(
               new FileReader( "Example6.xml" )) );

         //将圆形对象显示到标准输出．．．
         Circle c;
         Vector items = ex6.getCircles();
         Enumeration e = items.elements();
         while( e.hasMoreElements()){
                           c = (Circle) e.nextElement();
            c.print( System.out );
         }
         // // 将长方形对象显示到标准输出．．．
         Square s;
         items = ex6.getSquares();
         e = items.elements();
         while( e.hasMoreElements()){
                           s = (Square) e.nextElement();
            s.print( System.out );
         }

        // 将三角形对象显示到标准输出．．．
         Triangle t;
         items = ex6.getTriangles();
         e = items.elements();
         while( e.hasMoreElements()){
                           t = (Triangle) e.nextElement();
            t.print( System.out );
         }

      }catch ( Exception e )  {
         e.printStackTrace();
      }
   }
}
(未完待续)

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