tiptestservlet.java

高级java2 大学教程(含源码,经典的Java学习教程

      // handle exception building Document
      catch ( ParserConfigurationException parserException ) {
         parserException.printStackTrace();
      }

      return null;

   } // end method createXMLTipTestQuestion

   // send tip test to J2ME client
   private void sendJ2MEClientResponse( ResultSet resultSet,
      HttpServletRequest request,
      HttpServletResponse response ) throws IOException
   {
      // convert ResultSet to two-dimensional String array
      String resultTable[][] = getResultTable( resultSet );

      // create random-number generator
      Random random = new Random( System.currentTimeMillis() );

      // create 4 random tips
      int randomRow[] = getRandomIndices( random );

      // randomly determine correct index from 4 random indices
      int correctAnswer = Math.abs( random.nextInt() ) % 
         randomRow.length;

      int correctRow = randomRow[ correctAnswer ];

      // open old session
      HttpSession session = request.getSession();

      // store correct answer in session
      session.setAttribute( "correctAnswer", 
         new Integer( correctAnswer ) );

      // store correct tip name in session
      session.setAttribute( "correctTipName", new String( 
         resultTable[ correctRow ][ 1 ] ) );

      // store correct tip description in session
      session.setAttribute( "correctTipDescription", new String( 
         resultTable[ correctRow ][ 2 ] ) );

      // send J2ME client image name
      String imageName = "/j2me/images/"  + 
         resultTable[ correctRow ][ 3 ] + ".png";

      response.setContentType( "text/plain" );
      PrintWriter out = response.getWriter();
      out.println( imageName );

      // send J2ME client test
      for ( int i = 0; i < randomRow.length; i++ )
         out.println( resultTable[ randomRow[ i ] ][ 4 ] );

   } // end method sendJ2MEClientResponse

   // convert ResultSet to two-dimensional String array
   private String[][] getResultTable( ResultSet resultSet )
   {
      // create table of Strings to store ResultSet
      String resultTable[][] = new String[ 7 ][ 5 ];

      for ( int i = 0; i < 7; i++ ) {

         for ( int j = 0; j < 5; j++ )
            resultTable[ i ][ j ] = "";
      }

      // store all columns in table
      try {

         // for each row in resultSet
         for ( int row = 0; resultSet.next(); row++ ) {

            // for each column in resultSet
            for ( int column = 0; column < 5; column++ ) {

               // store resultSet element in resultTable
               resultTable[ row ][ column ] += 
                  resultSet.getObject( column + 1 );
            }
         }
      }

      // handle exception if servlet cannot get ResultSet Object
      catch ( SQLException sqlException ) {
         sqlException.printStackTrace();
         return null;
      }

      return resultTable;

   } // end method getResultTable

   // get 4 randomly generated indices from resultTable
   private int[] getRandomIndices( Random random )
   {
      // create list containing row indices for resultTable
      int list[] = new int[ 7 ];

      for ( int i = 0; i < list.length; i++ )
         list[ i ] = i;

      int randomRow[] = new int[ 4 ];

      // select 4 randomly generated indices from list
      for ( int i = 0; i < randomRow.length; i++ )
         randomRow[ i ] = getRandomRow( list, random );

      return randomRow; // return these indices

   } // end method getRandomIndices

   // get random element from list, then nullify element
   private int getRandomRow( int list[], Random random )
   {
      // get random element from list
      int randomRow = Math.abs( random.nextInt() ) % list.length;

      while ( list[ randomRow ] < 0 )
         randomRow = Math.abs( random.nextInt() ) % list.length;

      list[ randomRow ] = -1; // nullify element

      return randomRow;

   } // end method getRandomRow

   // apply XSLT style sheet to XML document
   private void applyXSLT( String xslFile,
      Document xmlDocument, HttpServletResponse response )
      throws IOException
   {
      // apply XSLT
      try {

         // open InputStream for XSL document 
         InputStream xslStream = 
            getServletContext().getResourceAsStream( xslFile );

         // create StreamSource for XSLT document
         Source xslSource = new StreamSource( xslStream );

         // create DOMSource for source XML document
         Source xmlSource = new DOMSource( xmlDocument );

         // get PrintWriter for writing data to client
         PrintWriter output = response.getWriter();

         // create StreamResult for transformation result
         Result result = new StreamResult( output );

         // create Transformer for XSL transformation
         Transformer transformer =
            transformerFactory.newTransformer( xslSource );

         // transform and deliver content to client
         transformer.transform( xmlSource, result );

      } // end try

      // handle exception transforming content
      catch ( TransformerException exception ) {
         exception.printStackTrace();
      }

   } // end method applyXSLT

   // create XML Document that stores Tip Test answer
   private Document createXMLTipTestAnswer( 
      HttpServletRequest request ) throws IOException
   {
      // get session
      HttpSession session = request.getSession();

      // match correct answer with session answer
      Integer integer = 
         ( Integer ) session.getAttribute( "correctAnswer" );
      int correctAnswer = integer.intValue();

      // give client correct tip name and description
      String correctTipName = 
         ( String ) session.getAttribute( "correctTipName" );

      String correctTipDescription = 
         ( String ) session.getAttribute( 
            "correctTipDescription" );

      // get user selection
      int selection = Integer.parseInt( 
         request.getParameter( "userAnswer" ) );

      String answer;

      // determine if user answer is correct
      if ( correctAnswer == selection )
         answer = "Correct";
      else
         answer = "Incorrect";

      // get link to TipTestServlet
      String servletName = request.getContextPath() + "/" +
         getServletConfig().getServletName();

      // create XML document based on randomly determined info
      try {

         // create document
         DocumentBuilder builder = factory.newDocumentBuilder();
         Document document = builder.newDocument();

         // create question root Element
         Element root = document.createElement( "answer" );
         document.appendChild( root );

         // append Element that informs client of correct answer
         Element correct = document.createElement( "correct" );
         correct.appendChild( 
            document.createTextNode( answer ) );
         root.appendChild( correct );

         // append Element that describes tip name
         Element name = 
            document.createElement( "correctTipName" );
         name.appendChild( 
            document.createTextNode( correctTipName ) );
         root.appendChild( name );

         // append Element that describes tip description
         Element description = 
            document.createElement( "correctTipDescription" );
         description.appendChild( 
            document.createTextNode( correctTipDescription ) );
         root.appendChild( description );

         // append Element that links to TipTestServlet
         Element servletLink = 
            document.createElement( "servletName" );
         servletLink.appendChild( 
            document.createTextNode( servletName ) );
         root.appendChild( servletLink );

         return document;

      } // end try

      // handle exception building Document
      catch ( ParserConfigurationException parserException ) {
         parserException.printStackTrace();
      }

      return null;

   } // end method createXMLTipTestAnswer

   // send answer to J2ME client
   private void sendJ2MEAnswer( HttpServletRequest request,
      HttpServletResponse response ) throws IOException
   {
      // get client test response
      BufferedReader in = request.getReader();
      int selection = Integer.parseInt( in.readLine().trim() );

      // send J2ME client text data
      response.setContentType( "text/plain" );
      PrintWriter out = response.getWriter();

      // inform client whether client is correct or incorrect
      HttpSession session = request.getSession();

      // match correct answer with session answer
      Integer integer = 
         ( Integer ) session.getAttribute( "correctAnswer" );
      int correctAnswer = integer.intValue();

      // send correct tip name and description
      String correctTipName = 
         ( String ) session.getAttribute( "correctTipName" );

      String correctTipDescription = 
         ( String ) session.getAttribute( 
            "correctTipDescription" );

      // determine whether answer is correct
      if ( selection == correctAnswer )
         out.println( "Correct" );
      else
         out.println( "Incorrect" );

      // give client correct tip name and description
      out.println( correctTipName );
      out.println( correctTipDescription );

   } // end method sendJ2MEAnswer

   // invoked when servlet is destroyed
   public void destroy()
   {
      // close database connection
      try {
         connection.close();
      }

      // handle if connection cannot be closed
      catch ( SQLException sqlException ) {
         sqlException.printStackTrace();
      }

   } // end method destroy
}

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