SwingWorker JavaDB Concurrency problems

Question

I have an application that computes statistics from values stored in a JavaDB database. I am trying to implement batch job functionality that will allow users to quickly run multiple analyses without the point-and-click of the GUI. Each analysis extends SwingWorker, which adds text to a JTextArea when the done() method is called. My problem is that I get a "java.sql.SQLException: No suitable driver found for jdbc:derby:C:/mydatabase" SQL exception sometimes. the code below illustrates my problem. I'm guessing that this is a concurrency issue, but I don't know how to fix it. Any suggestion?
The GUI class is:
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class MyGui extends JFrame{
     private static final long serialVersionUID = 1L;
     JTextField text = null;
     JPanel main = null;
     String connectionString = "jdbc:derby:C:/mydatabase";
     String tableName="MYTABLE";
     String selectStatement = "SELECT * FROM " + tableName;
     public MyGui(){
          super("Concurrency Test");
          this.setPreferredSize(new Dimension(300,100));
          getContentPane().add(getPanel());
     public JPanel getPanel(){
          JPanel main = new JPanel();
          main.setLayout(new GridLayout(1,1));
          text = new JTextField(30);
          text.setText("Start");
          main.add(text, BorderLayout.CENTER);
          return main;
     public void readDatabase(){     
          int count=0;
          for(int i=0;i<10000;i++){
               count++;
               try{
                    ConnectAndRead reader =  new ConnectAndRead(connectionString, selectStatement, text, count);
                    reader.execute();
               }catch(Exception ex){
     public static void main(String[] args) {
          MyGui gui = new MyGui();
          gui.pack();
          gui.setVisible(true);
          gui.setResizable(false);
          gui.readDatabase();
}And the Database connection class is:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.swing.JTextField;
import javax.swing.SwingWorker;
public class ConnectAndRead extends SwingWorker<String, Void>{
     String connectionString="";
     String selectStatement="";
     JTextField text=null;
     int count = 0;
     public ConnectAndRead(String connectionString, String selectStatement, JTextField text, int count){
          this.connectionString=connectionString;
          this.selectStatement=selectStatement;
          this.text=text;
          this.count=count;
     public String connectAndRead()throws SQLException{
          Connection conn = null;
          try{
               conn = DriverManager.getConnection(connectionString);
               Statement stmt=conn.createStatement(ResultSet.CONCUR_READ_ONLY, ResultSet.TYPE_SCROLL_INSENSITIVE);
               ResultSet rs = stmt.executeQuery(selectStatement);
               rs.close();
               stmt.close();
               conn.close();
               String text = "Database access " + count + "(should be 10,000)";
               return text;
          }catch(SQLException ex){
               count--;
               throw new SQLException(ex);
     protected String doInBackground() {
          String s = "";
          try{
               s = connectAndRead();
          }catch(SQLException ex){
               ex.printStackTrace();
          return s;
     @Override
     protected void done(){
          try{
               text.setText(get());
          }catch(Exception ex){
               ex.printStackTrace();
}

Answer 1

I believe I found the solution to my problem. It is posted here [http://forum.java.sun.com/thread.jspa?threadID=5298060&tstart=0] . Sorry for the cross posting.