Catching jsp/tomcat/java SQL error

Question

I have been trying to get the sample code to work from an old book. I was finally able to get it to run under tomcat 4.1.31 but there is one bug I just cannot figure out how to handle. I am a beginner to Java/JSP/Tomcat and have about 16+ hours invested in this problem so far.
The delFruit.jsp calls methods from FruitConnect.java.
I found that if the fruit chosen for deletion was not involved in a referential integrity link to a FruitMonth file the code works fine. But if it is linked the delFruit.jsp just displays a blank screen and nothing is deleted. It is fine for it not to be deleted but I cannot find anyway to handle it. I tried to add the checkFruitForSale bandaid below but it causes me a blank screen as well.
Any help would be appreciated.
It would be great if I could just see what is happening when FruitConnect is processing code. I get no errors, just a blank screen. I'm going to try using NetBeans and their debugger next.
Here is delFruit:
<%@ page import="java.sql.*" %>
<jsp:include page="adminHeader.html" flush="true" />
<jsp:useBean id="fruitConnect" class="fruit1.FruitConnect" />
<%
String msg = "The following fruits have been deleted:<br> ";
//Build the list of fruits to delete
String delFruit[] = request.getParameterValues("delFruit");
//WE WILL ONLY GET CHECKBOXES THAT WERE CHECKED
   String fruitList = "";
   if (delFruit != null){
     int len = delFruit.length;
     fruitConnect.dbConnect();
     for (int i = 0; i < len; i++) {
          String passfruit = delFruit;
          if (fruitConnect.checkFruitForSale(passfruit)) {}
          else{
          fruitList = fruitList + "'" + delFruit[i] + "',";
          msg = msg + delFruit[i] + "<br>";
          out.print(msg);
          out.print(msg);
     fruitList = fruitList + "'nonsense'";
     if (fruitConnect.deleteFruit(fruitList) < 1) {
          msg = "There was an error deleting the fruits from the database.";
     else{
     msg = "Deletion was successful";
     fruitConnect.dbDisconnect();
else {
     msg = "You must select some fruit to delete.";
%>
HERE IS FruitConnect.java
package fruit1;
import java.sql.*;
public class FruitConnect {
   private Driver drv = null;
   private Connection conn = null;
   private ResultSet rs = null;
   private Statement stmt = null;
   public FruitConnect(){}
   public void dbConnect() throws Exception{
//      drv = (Driver) Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newInstance();
//      conn = DriverManager.getConnection("jdbc:odbc:Fruit");
try{
      drv = (Driver) Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newInstance();
      conn = DriverManager.getConnection("jdbc:odbc:Fruit");
catch ( SQLException sqlException)
sqlException.printStackTrace();
finally
try{
catch (Exception exception)
   public boolean getNextItem() throws Exception{
      boolean ret = rs.next();
      return(ret);
   public String getItemNameString(String columnName) throws Exception{
      String name = rs.getString(columnName);
      return(name);
   public float getItemNameFloat(String columnName) throws Exception{
      float name = rs.getFloat(columnName);
      return(name);
   public boolean selectFruits() throws Exception{
      String query = "SELECT Id, Name FROM Fruit";
      stmt = conn.createStatement();
      rs = stmt.executeQuery(query);
      boolean ret = false;
      if (rs != null)
         ret = true;
      return(ret);
   public boolean selectMonths() throws Exception{
      String query = "SELECT Id, Name FROM Month";
      stmt = conn.createStatement();
      rs = stmt.executeQuery(query);
      boolean ret = false;
      if (rs != null)
         ret = true;
      return(ret);
   public boolean selectFruitForSale() throws Exception{
      String query = "SELECT F.Name AS Fruit, M.Name AS Month, Price, Weight, (Price * Weight) AS TotalPrice FROM FruitMonth AS FM, Fruit AS F, Month AS M WHERE FM.FruitId = F.Id AND FM.MonthId = M.Id ORDER BY M.Id";
      stmt = conn.createStatement();
      rs = stmt.executeQuery(query);
      boolean ret = false;
      if (rs != null)
         ret = true;
      return(ret);
   public int insertFruit(String name) throws Exception{
      String query = "INSERT INTO Fruit (Name) VALUES ('" + name + "')";
      stmt = conn.createStatement();
      int ret = stmt.executeUpdate(query);
      return(ret);
   public int insertFruitForSale(String insertValues) throws Exception{
      String query = "INSERT INTO FruitMonth (FruitId, MonthId, Price, Weight) VALUES (" + insertValues + ")";
      stmt = conn.createStatement();
      int ret = stmt.executeUpdate(query);
      return(ret);     
   public int deleteFruit(String fruitList) throws Exception{
      String query = "DELETE FROM Fruit WHERE Name IN (" + fruitList + ")";
      stmt = conn.createStatement();
      int ret = stmt.executeUpdate(query);
      return(ret);
   public void dbDisconnect() throws Exception{
      stmt.close();
      conn.close();
   public boolean checkFruitForSale(String thisfruit) throws Exception{
      String query = "SELECT F.Name AS Fruit, M.Name AS Month, Price, Weight, (Price * Weight) AS TotalPrice FROM FruitMonth AS FM, Fruit AS F, Month AS M WHERE FM.FruitId = F.Id AND FM.MonthId = M.Id AND F.Name IN (" + thisfruit + ") ORDER BY M.Id";
try{
      stmt = conn.createStatement();
      rs = stmt.executeQuery(query);
catch ( SQLException sqlException)
sqlException.printStackTrace();
      boolean ret = false;
      if (rs != null)
         ret = true;
      return(ret);
finally
try{
catch (Exception exception)
      boolean ret = false;
      if (rs != null)
         ret = true;
      return(ret);
   public String Check1(String columnName) throws Exception{
      String name = rs.getString(columnName);
      return(name);

Answer 1

First thing to check would be the Tomcat log file. Most likely there is an error message printed there:
Look in [TOMCAT]/logs for any files modified recently. Open it, and you should find some hints as to your error.
It would be great if I could just see what is happening when
FruitConnect is processing code.For that sort of thing, you want to use a logger. Either Log4J or the standard Java1.4 logger would help. Basically configure it to log statements to file as your program runs.
I get no errors, just a blank screenThat could indicate that the page ran enough to fill up the page buffer, and then failed. When you view source, do you see anything on the page at all?