// 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!" );
out.println( "" );
out.println( "" );
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( "Error" );
out.println( "" );
out.println( "Database error occurred. " );
out.println( "Try again later.