// Fig. 26.20: SurveyServlet.java
// A Web-based survey that uses JDBC from a servlet.
package com.deitel.jhtp6.servlets;
import java.io.*;
import java.text.*;
import java.sql.*;
import javax.sql.*;
import javax.naming.*;
import javax.servlet.*;
import javax.servlet.http.*;
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 {
// System.setProperty( "db2j.system.home",
// config.getInitParameter( "databaseLocation" ) );
// Class.forName( config.getInitParameter( "databaseDriver" ) );
// connection = DriverManager.getConnection(
// config.getInitParameter( "databaseName" ) );
// create Statement to query database
// statement = connection.createStatement();
// Obtain environment naming context
InitialContext ic = new InitialContext();
// Look up our data source
DataSource ds = ( DataSource ) ic.lookup(
"java:comp/env/jdbc/survey" );
// Allocate and use a connection from the pool
connection = ds.getConnection();
// 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 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( "" );
out.println( "" );
out.println(
"" );
// head section of document
out.println( "" );
// read current survey response
int value =
Integer.parseInt( request.getParameter( "animal" ) );
String query;
// attempt to process a vote and display current results
try {
// update total for current survey response
query = "UPDATE surveyresults SET votes = votes + 1 " +
"WHERE id = " + value;
statement.executeUpdate( query );
// get total of all survey responses
query = "SELECT sum( votes ) FROM surveyresults";
ResultSet totalRS = statement.executeQuery( query );
totalRS.next();
int total = totalRS.getInt( 1 );
// get results
query = "SELECT surveyoption, votes, id FROM surveyresults " +
"ORDER BY id";
ResultSet resultsRS = statement.executeQuery( query );
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.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( "" );
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.