程序目的:
从一个xml file读取相关信息,然后输出结果并生成新的xml file. 采用SAX Version 2,

怀疑问题出在这部分代码里:
import java.io.*;
import org.xml.sax.*;
import org.xml.sax.helpers.*;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;

public class bookSAXApp extends DefaultHandler
{
  ............

public static void main (String args[]) throws Exception
  {
      try {
                XMLReader saxParser= XMLReaderFactory.createXMLReader();//creating an xml reader        

               bookSAXApp handler = new bookSAXApp();   
               saxParser.setContentHandler(handler);
              saxParser.setErrorHandler(handler);

            FileReader reader = new FileReader("bookInstance.xml");
           saxParser.parse( new InputSource(reader));
                
         PrintWriter toFile=new PrintWriter(new FileWriter("interBooks.xml"));
         toFile.println(xmlContent);
         toFile.close();
      }
      catch ( SAXParseException spe ) {
         System.err.println( "Parse Error: " + spe.getMessage() );
      }
    
      catch ( SAXException se ) {
         se.printStackTrace();
      }
      catch ( IOException e ) {
         e.printStackTrace();
      }
   
    }    

    * -Dorg.xml.sax.driver=org.apache.xerces.parsers.SAXParser if you're use xerces.
      Alternatives:

-Djavax.xml.parsers.DocumentBuilderFactory=org.apache.xerces.jaxp.DocumentBuilderFactoryImpl
-Djavax.xml.parsers.SAXParserFactory=org.apache.xerces.jaxp.SAXParserFactoryImpl

    * -Dorg.xml.sax.driver=org.apache.crimson.parser.XMLReaderImpl if you're use crimson.
    * Make sure xerces.jar or crimson.jar or something similar on your classpath

BTW, you can specify Transformer too the same fashion.

    * javax.xml.transform.TransformerFactory = org.apache.xalan.processor.TransformerFactoryImpl if you're using xalan
    * javax.xml.transform.TransformerFactory = com.icl.saxon.TransformerFactoryImpl if you're using saxon
    * Make sure xalan.jar or saxon.jar or something similar on your classpath