Update functionality error

From: Mohammed Mazid (kadmazid_at_hotmail.com)
Date: 03/29/04 

Date: 29 Mar 2004 01:57:37 -0800

Can anyone please help me here? Basically I have modified the source
code and understood it but when I update a record in the db using a
JSP, it gives me an error "The flight you selected does exist."

Althought there is not selection going on, instead it is entered, I
need it to match the flight in the db using the flightNo. I want all
the attributes to be changed apart from the flightNo itself as it is
it's associated details I need changing (i.e. flightdate, destination,
arrTime and depTime).

Below are the code snippets but did not include everything as all
details were not neded. Therefore I had put part of it. But
somewhere I am going wrong of "updating" a db record.

public class Flight
{
  String flightNo;
  Date flightDate;
  String destination;
  Time arrTime;
  Time depTime;

  Flight(String flightNo, Date flightDate, String destination, Time
arrTime, Time depTime)
  {
   this.flightNo = flightNo;
   this.flightDate = flightDate;
   this.destination = destination;
   this.arrTime = arrTime;
   this.depTime = depTime;
  }

  public String getFlight()
  {
    return flightNo;
  }
  public Date getFlightDate()
  {
    return flightDate;
  }
  public String getDestination()
  {
    return destination;
  }
  public Time getArrTime()
  {
    return arrTime;
  }
  public Time getDepTime()
  {
    return depTime;
  }
  public String toString()
  {
    return flightNo;
  }
}

public class FlightService
{
  private FlightDAO flightDataAccess;

  public FlightService()
  { flightDataAccess = new FlightDAO(); }

  public Flight getFlight(String flightNo)
  {
    Flight flight = null;

    try
    {
      flight = flightDataAccess.retrieve(flightNo);
    }
    catch (ObjectNotFoundException onfe) { flight = null; }

    return flight;
  }

  public Flight updateFlight(String flightNo, Date flightDate, String
destination, Time depTime, Time arrTime)
  {
   Flight flight = new Flight(flightNo, flightDate, destination,
          depTime, arrTime);

  // Perform the DB transaction
  flightDataAccess.update(flight);

  return flight;
  }
}

class FlightDAO
{
  FlightDAO() {}

  Flight retrieve(String flightNo)
         throws ObjectNotFoundException {

    // Assume everything is declared

    try
        {
      // Get a database connection
      connection = connectionPool.getConnectionNoWait();

      // Create SQL SELECT statement
      stmt = connection.prepareStatement(RETRIEVE_STMT);

      // Initialize statement and execute the query
      stmt.setString(1, flightNo);
      results = stmt.executeQuery();

      // Iterator over the query results
      while ( results.next() )
          {
        // We expect only one row to be returned
        num_of_rows++;
        if ( num_of_rows > 1 )
                {
          throw new SQLException("Too many rows were returned.");
        }

        // Create and fill-in the Flight object
        flight = new Flight(results.getString("FlightNo"),
                            results.getDate("FlightDate"),
                            results.getString("Destination"),
                            results.getTime("ArrivalTime"),
                            results.getTime("DepartureTime"));
      }

      if ( flight != null ) { return flight; }
      else { throw new ObjectNotFoundException(); }

    // Handle any SQL errors
    }
        catch (SQLException se)
        {
      throw new RuntimeException("A database error occured. " +
        se.getMessage());

//Some more catch statements and finally blocks exist.
  }

  private static final String RETRIEVE_STMT
    = "SELECT FlightNo, FlightDate, Destination, ArrivalTime,
DepartureTime FROM Flight WHERE FlightNo = ?";

  void update(Flight flight) {

    // Assume all declared

    PreparedStatement update_stmt = null;

    try {
      // Get a database connection
      connection = connectionPool.getConnectionNoWait();

      // Create SQL INSERT statement
      update_stmt = connection.prepareStatement(UPDATE_STMT);

      // Add data fields
      update_stmt.setDate(1, flight.flightDate);
      update_stmt.setString(2, flight.destination);
      update_stmt.setTime(3, flight.arrTime);
          update_stmt.setTime(4, flight.depTime);

      // Execute SQL INSERT statement
      update_stmt.executeUpdate();

    // Handle any SQL errors
    }
        catch (SQLException se)
        {
      throw new RuntimeException("A database error occured. " +
se.getMessage());

//Assume catch and finally block exist
      }
    }
  }

private static final String UPDATE_STMT
 = "UPDATE Flight SET FlightDate = ?, Destination = ?, ArrivalTime =
?, DepartureTime = ? WHERE FlightNo = ?";
}

//Assume all imports exist

public final class FlightServlet extends HttpServlet
{
  public void doPost(HttpServletRequest request,
HttpServletResponse response)
         throws IOException, ServletException {

    processRequest(request, response);
  }

  public void processRequest(HttpServletRequest request,
                             HttpServletResponse response)
         throws IOException, ServletException {
    // Declare the dispatcher for the View
    RequestDispatcher view = null;

    // Declare service and database variables
    FlightService flightSvc;
    Flight flight = null;

    // Create the status object and store i tin the request for use
    // by the 'Error Page' View (if necessary)
    Status status = new Status();
    request.setAttribute("status", status);

    // Extract HTML form parameters
    String flightNo = request.getParameter("flightNo");
            
        String dateString = request.getParameter("flightDate");
        Date flightDate = Date.valueOf(dateString);
                        
        String destination = request.getParameter("destination");

        String timeString = request.getParameter("depTime");
        Time depTime = Time.valueOf(timeString + ":00");

        String timeStr = request.getParameter("arrTime");
        Time arrTime = Time.valueOf(timeStr + ":00");

    // Assume there are if-else statements

    // Now delegate the real work to the FlightService object
    try
        {
      // Create the "flight service" object
      flightSvc = new FlightService();

      // Check if this flight object already exists
      flight = flightSvc.getFlight(flightNo);
      if ( flight != null )
          {
        status.addException(
            new Exception("The flight you selected already exists;"));
      }

      // If any of the above verification failed, then return the
      // 'Update Flight Form' View and return without proceeding with
the
      // rest of the business logic
      if ( ! status.isSuccessful() ) {
        view = request.getRequestDispatcher("updateform.jsp");
        view.forward(request, response);
        return;
      }

      // Add the flight to the data-file
      flight = flightSvc.updateFlight(flightNo, flightDate,
destination,
          depTime, arrTime);
      request.setAttribute("flight", flight);

      // The flight update process was successful,
      // forward to the 'Flight Updated' View
      view = request.getRequestDispatcher("thank_you.jsp");
      view.forward(request, response);

    // Handle any business logic errors
    } catch (Exception e) {
      status.addException(e);
      view = request.getRequestDispatcher("updateform.jsp");
      view.forward(request, response);
    }
  }
}

Can anyone please suggest where to change and what would be the
correct code fragment? I'd be really appreciated. Thanks for your
contribution.

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