// Fig. 26.21: SurveyServlet.java // A Web-based survey that uses JDBC from a servlet. package com.deitel.jhtp6.servlets; import java.io.PrintWriter; import java.io.IOException; import java.sql.Connection; import java.sql.DriverManager; import java.sql.Statement; import java.sql.ResultSet; import java.sql.SQLException; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.UnavailableException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class SurveyServlet extends HttpServlet { private Connection connection; private Statement statement; // set up database connection and create SQL statement public void init( ServletConfig config ) throws ServletException { // attempt database connection and create Statement try { Class.forName( config.getInitParameter( "databaseDriver" ) ); connection = DriverManager.getConnection( config.getInitParameter( "databaseName" ), config.getInitParameter( "username" ), config.getInitParameter( "password" ) ); // create Statement to query database statement = connection.createStatement(); } // end try // 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 catch } // end method init // 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(); // start XHTML document out.println( "" ); out.printf( "%s%s%s", "\n" ); out.println( "" ); // head section of document out.println( "
" ); // read current survey response int value = Integer.parseInt( request.getParameter( "animal" ) ); String sql; // attempt to process a vote and display current results try { // update total for current survey response sql = "UPDATE surveyresults SET votes = votes + 1 " + "WHERE id = " + value; statement.executeUpdate( sql ); // get total of all survey responses sql = "SELECT sum( votes ) FROM surveyresults"; ResultSet totalRS = statement.executeQuery( sql ); totalRS.next(); // position to first record int total = totalRS.getInt( 1 ); // get results sql = "SELECT surveyoption, votes, id FROM surveyresults " + "ORDER BY id"; ResultSet resultsRS = statement.executeQuery( sql ); out.println( "Thank you for participating." );
out.println( "
Results:
" ); // process results int votes; while ( resultsRS.next() ) { out.print( resultsRS.getString( 1 ) ); out.print( ": " ); votes = resultsRS.getInt( 2 ); out.printf( "%.2f", ( double ) votes / total * 100 ); out.print( "% responses: " ); out.println( votes ); } // end while resultsRS.close(); out.print( "Total responses: " ); out.print( total ); // end XHTML document out.println( "" ); out.close(); } // end try // if database exception occurs, return error page catch ( SQLException sqlException ) { sqlException.printStackTrace(); out.println( "
Database error occurred. " ); out.println( "Try again later.