hi all. I find myself in need of help/assistance with a longtime problem
of mine and that is how do you get a servlet working with a backend
database server?? Here is the basic SurveyServlet.java servlet and
please notice that the database server in question is IBM's Cloudscape .
after the servlet I have the html file which the servlet is supposed to
work with. thanx in advance for anyone's help.
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 survey 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
}
the html file :
<?xml version = "1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd";>
<!-- Survey.html -->
<html xmlns = "http://www.w3.org/1999/xhtml";>
<head>
<title>Survey</title>
</head>
<body>
<form method = "post" action = "/animalsurvey">
<p>What is your favorite pet?</p>
<p>
<input type = "radio" name = "animal"
value = "1" />Dog<br />
<input type = "radio" name = "animal"
value = "2" />Cat<br />
<input type = "radio" name = "animal"
value = "3" />Bird<br />
<input type = "radio" name = "animal"
value = "4" />Snake<br />
<input type = "radio" name = "animal"
value = "5" checked = "checked" />None
</p>
<p><input type = "submit" value = "Submit" /></p>
</form>
</body>
</html>
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