📄 surveyservlet.java

📁 java web services how to program
💻 JAVA
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// Fig. A.26: SurveyServlet.java
// A Web-based survey that uses JDBC from a servlet.
package com.deitel.jws.servlets;

import java.io.*;
import java.text.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class SurveyServlet extends HttpServlet {
   private Connection connection;
   private PreparedStatement updateVotes, totalVotes, results;

   // set up database connection and prepare SQL statements
   public void init( ServletConfig config ) 
      throws ServletException
   {
      // attempt database connection and create PreparedStatements
      try {
         Class.forName( "COM.cloudscape.core.RmiJdbcDriver" );
         connection = DriverManager.getConnection(
            "jdbc:rmi:jdbc:cloudscape:animalsurvey" );

         // PreparedStatement to add one to vote total for a 
         // specific animal 
         updateVotes =
            connection.prepareStatement(
               "UPDATE surveyresults SET votes = votes + 1 " +
               "WHERE id = ?"
            );

         // PreparedStatement to sum the votes
         totalVotes =
            connection.prepareStatement(
               "SELECT sum( votes ) FROM surveyresults"
            );

         // PreparedStatement to obtain surveyoption table's data
         results =
            connection.prepareStatement(
               "SELECT surveyoption, votes, id " +
               "FROM surveyresults ORDER BY id"
            );
      }
      
      // for any exception throw an UnavailableException to 
      // indicate that the servlet is not currently available
      catch ( Exception exception ) {
         exception.printStackTrace();
         throw new UnavailableException(exception.getMessage());
      }

   }  // end of init method

   // process survey response
   protected void doPost( HttpServletRequest request,
      HttpServletResponse response )
         throws ServletException, IOException
   {
      // set up response to client
      response.setContentType( "text/html" ); 
      PrintWriter out = response.getWriter();
      DecimalFormat twoDigits = new DecimalFormat( "0.00" );

      // start XHTML document
      out.println( "<?xml version = \"1.0\"?>" );

      out.println( "<!DOCTYPE html PUBLIC \"-//W3C//DTD " +
         "XHTML 1.0 Strict//EN\" \"http://www.w3.org" +
         "/TR/xhtml1/DTD/xhtml1-strict.dtd\">" ); 

      out.println( 
         "<html xmlns = \"http://www.w3.org/1999/xhtml\">" );

      // head section of document
      out.println( "<head>" );  
      
      // read current survey response
      int value = 
         Integer.parseInt( request.getParameter( "animal" ) );

      // attempt to process a vote and display current results
      try {

         // update total for current surevy response
         updateVotes.setInt( 1, value );
         updateVotes.executeUpdate();

         // get total of all survey responses
         ResultSet totalRS = totalVotes.executeQuery();
         totalRS.next();
         int total = totalRS.getInt( 1 );

         // get results
         ResultSet resultsRS = results.executeQuery();
         out.println( "<title>Thank you!</title>" );
         out.println( "</head>" );  
         
         out.println( "<body>" );  
         out.println( "<p>Thank you for participating." );
         out.println( "<br />Results:</p><pre>" );
         
         // process results
         int votes;
         
         while ( resultsRS.next() ) {
            out.print( resultsRS.getString( 1 ) );
            out.print( ": " );
            votes = resultsRS.getInt( 2 );
            out.print( twoDigits.format( 
               ( double ) votes / total * 100 ) );
            out.print( "%  responses: " );
            out.println( votes );
         }

         resultsRS.close();
         
         out.print( "Total responses: " );
         out.print( total );
         
         // end XHTML document
         out.println( "</pre></body></html>" );         
         out.close();
      }

      // if database exception occurs, return error page
      catch ( SQLException sqlException ) {
         sqlException.printStackTrace();
         out.println( "<title>Error</title>" );
         out.println( "</head>" );  
         out.println( "<body><p>Database error occurred. " );
         out.println( "Try again later.</p></body></html>" );
         out.close();
      }

   }  // end of doPost method

   // close SQL statements and database when servlet terminates
   public void destroy()
   {
      // attempt to close statements and database connection
      try {
         updateVotes.close();
         totalVotes.close();
         results.close();
         connection.close();
      }

      // handle database exceptions by returning error to client
      catch( SQLException sqlException ) {
         sqlException.printStackTrace();
      }
   }  // end of destroy method
}
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