请注意看参数

SAXParserFactory saxParserFactory = SAXParserFactory.newInstance();

SAXParser saxParser = saxParserFactory.newSAXParser();

SaxParserHandler saxParserHandler = new SaxParserHandler();

saxParser.parse("books.xml", saxParserHandler);

//parse（） 

public void parse(String uri, DefaultHandler dh)

        throws SAXException, IOException {

        if (uri == null) {

            throw new IllegalArgumentException("uri cannot be null");

        }

        InputSource input = new InputSource(uri);

        this.parse(input, dh);//------------执行到此处

    }

public void parse(InputSource is, DefaultHandler dh)

        throws SAXException, IOException {

        if (is == null) {

            throw new IllegalArgumentException("InputSource cannot be null");

        }

        XMLReader reader = this.getXMLReader();

        if (dh != null) {

            reader.setContentHandler(dh);

            reader.setEntityResolver(dh);

            reader.setErrorHandler(dh);

            reader.setDTDHandler(dh);

        }

        reader.parse(is);//----------

    }

 public void parse (InputSource input)

        throws IOException, SAXException;

//----------

void org.xml.sax.XMLReader

 /**

     * Receive notification of the start of an element.

     *

     * <p>By default, do nothing.  Application writers may override this

     * method in a subclass to take specific actions at the start of

     * each element (such as allocating a new tree node or writing

     * output to a file).</p>

     *

     * @param uri The Namespace URI, or the empty string if the

     *        element has no Namespace URI or if Namespace

     *        processing is not being performed.

     * @param localName The local name (without prefix), or the

     *        empty string if Namespace processing is not being

     *        performed.

     * @param qName The qualified name (with prefix), or the

     *        empty string if qualified names are not available.

     * @param attributes The attributes attached to the element.  If

     *        there are no attributes, it shall be an empty

     *        Attributes object.

     * @exception org.xml.sax.SAXException Any SAX exception, possibly

     *            wrapping another exception.

     * @see org.xml.sax.ContentHandler#startElement

     */

    public void startElement (String uri, String localName,

                              String qName, Attributes attributes)

        throws SAXException

    {

        // no op

    }