Urgent help on database server.

[Nabeel Mukhtar Siddiqui" <nabeelmukhtar@xxxxxxxxx (Nabeel Mukhtar Siddiqui)]

I am not very experienced in Java programming and hence I am facing a
problem in implementing a simple mulithreaded database server. The server
connects to client side applets through sockets, receives the query from the
clients and returns the resultset in string format.This happens after every
5 seconds. I also tried to make the server multithreaded so that multiple
clients can be simultaneously serviced. This server runs on a Windows NT
machine (JDK 1.2). It works fine in the night time when very few clients
connect to the server however in the office hours when the no. of clients
reaches as high as 400, the server shuts down and the OS displays the
message that application java.exe has caused an access violation at the
memory address _______. This is very annoying and critical for me. I also
haven't worked on Windows NT. What may be the cause of the error? Below is
the partial code of the server (the rest is irrelavent). Please give me
suggestions, pointers etc on the cause of the problem. Also I have tried to
make the server multithreaded. Is it working so? Is the architecture good
enough to support multiple (almost 1000) clients simultaneously? How can I
improve on it? If any one needs more specific details please inform me, but
please do help me. It is very urgent.
Thank you.

import java.io.*;
import java.net.*;
import java.sql.*;

public class QueryServer implements Runnable {
    private Socket   connection;

    public void run() {
 ServerSocket server;
 int      counter = 1;

 try {

     // Step 1: Create a ServerSocket.
     server = new ServerSocket(5000, 1000);

     while (true) {

  // Step 2: Wait for a connection.
  connection = server.accept();

  Connect cc = new Connect(connection);

     }
 } catch (IOException e) {
     e.printStackTrace();
 }
    }

    public static void main(String args[]) {
 new Thread(new QueryServer()).start();
    }

    protected void finalize() {
 try {
     connection.close();
 } catch (IOException ioe) {
     ioe.printStackTrace();
 }
    }

}

class Connect extends Thread {
    private final String FIELD_SEPARATOR = "#";
    private final String COLUMN_SEPARATOR = "|";
    private final String ROW_SEPARATOR = "$";
    private String       query;
    private ResultSet    resultSet;
    private String       stringResultSet;
    Socket   client;
    DataOutputStream     output;
    DataInputStream      input;

    public Connect(Socket s) {    // constructor
 client = s;

 try {
     input = new DataInputStream(client.getInputStream());
     output = new DataOutputStream(client.getOutputStream());
 } catch (IOException e) {
     try {
  client.close();
     } catch (IOException ex) {
  System.out.println("Error while getting socket streams.."
       + ex);
     }

     return;
 }

 this.start();
    }

    public void run() {
 try {

     // get a request and parse it.
     while (true) {
  query = input.readUTF();
  System.out.println(query);
  accessDataBase(query);
  System.out.println(stringResultSet);
  output.writeUTF(stringResultSet);
     }
 } catch (IOException e) {
     System.out.println("I/O error " + e);
 } catch (Exception ex) {
     System.out.println("Exception: " + ex);
 }
    }

    private synchronized void accessDataBase(String query) {
 String url = "jdbc:odbc:sysdsn";

 try {

     // Load the jdbc-odbc bridge driver
     Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

     Connection con = DriverManager.getConnection(url, "", "");
     Statement  stmt = con.createStatement();

     resultSet = stmt.executeQuery(query);

     convertResultSetToStream();

     // Close the statement
     stmt.close();

     // Close the connection
     con.close();
 } catch (SQLException ex) {}
 catch (java.lang.Exception ex) {}
    }

    private void convertResultSetToStream() throws SQLException {
 StringBuffer      theResultSet = new StringBuffer();

 // Get the ResultSetMetaData.  This will be used for
 // the column headings
 ResultSetMetaData rsmd = resultSet.getMetaData();

 // Get the number of columns in the result set
 int    numCols = rsmd.getColumnCount();

 // append the column labels first.
 for (int column = 0; column < numCols; column++) {
     theResultSet.append(rsmd.getColumnLabel(column + 1));
     theResultSet.append(COLUMN_SEPARATOR);
 }

 theResultSet.append(FIELD_SEPARATOR);

 // now append the table values.
 while (resultSet.next()) {
     for (int i = 1; i <= numCols; i++) {
  theResultSet.append(resultSet.getString(i));
  theResultSet.append(COLUMN_SEPARATOR);
     }

     theResultSet.append(ROW_SEPARATOR);
 }

 stringResultSet = theResultSet.toString();
    }

    protected void finalize() {
 try {
     client.close();
 } catch (IOException ioe) {
     ioe.printStackTrace();
 }
    }
}



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