Can't Send More Than One Query To The Server (Using Jdbc And Ocsf)

hello,
i'm using JDBC and OCSF to make client-server connection including MySQL.
i'm now stuck at a very strange problem:
my server can receive either "select..." string, "insert..." string, "update..." string (those are treated as queries), or any other string, which is treated as a simple message to the server (i do nothing with in so far)

here is the code of the server:

Code:

public void handleMessageFromClient (Object msg1, ConnectionToClient client) {
            String msg=((String)msg1).toLowerCase();
            if ( !( msg.startsWith("select") || msg.startsWith("insert") ||
                    msg.startsWith("update") ) ) {
                System.out.println("Message received: " + msg + " from " + client);
                this.sendToAllClients(msg);
                return;
            }
            try {
                Class.forName("com.mysql.jdbc.Driver").newInstance();
            }
            catch (Exception ex) {
                System.out.println("Couldn't load MySQL driver...");
            }
            try {
                  Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/test","root","Braude");
                  System.out.println("Connected to the database");  // indication on server only
                  Statement st = conn.createStatement();
                  // user sent a "select" query
                  if (msg.startsWith("select")){
                      int isResultEmpty=1;  // for indicating if the query returned no results
                      ResultSet rs=st.executeQuery(msg);
                      ResultSetMetaData rsmd=rs.getMetaData();
                      int numOfCols=rsmd.getColumnCount();
                      Vector result=new Vector();
                      while (rs.next()){
                          String[] tuple=new String[numOfCols];
                          for (int i=1;i<=numOfCols;i++)
                              tuple[i-1]=rs.getString(i);
                          result.addElement(tuple);
                          isResultEmpty=0;  // indicating at least one tuple in the result
                      }
                      if (isResultEmpty==0)
                          this.sendToAllClients(result);
                      else
                          this.sendToAllClients("No appropriate results!");
                      rs.close();
                  }  // end of select case

                  // if user tries to only update the db (no resultset is returned)
                  if (msg.startsWith("insert")  ||  msg.startsWith("update") ){
                      st.executeUpdate(msg);
                      this.sendToAllClients("Action successful!!");
                  }  // end of update case
                  st.close();
                  conn.close();
            }  // end of try
            catch (SQLException ex) { // handle any errors
                    this.sendToAllClients("SQLException: " + ex.getMessage());
                    this.sendToAllClients("SQLState: " + ex.getSQLState());
                    this.sendToAllClients("VendorError: " + ex.getErrorCode());
            }

  } // end of function

the problem is as follows:
if i send any series of simple messages (one or more), everything works fine.
when i send my first query (any of them, select / update / insert) , it executes.
but, after i send the first query, trying to send any message (query / simple one) ,
i get an error message, thrown by this code:

Code:

public void handleMessageFromClientUI(String message)
  {
    try
    {
        sendToServer(message);
    }
    catch(IOException e)
    {
      clientUI.display
        ("Could not send message to server.  Terminating client.");
      quit();
    }
  }

the sendToServer() method is inherited from the OCSF, i didn't touch it.
For conclusion, the problem is:
after sending simple messages, all fine. after sending a query, nothing else can be sent.
any idea will be very appreciated, I don't have a clue about what's wrong here..

 

P.S.
here is the stack trace of the exception:

Code:

java.net.SocketException: socket does not exist 
at ocsf.client.AbstractClient.sendToServer(AbstractClient.java:141) 
at client.ChatClient.handleMessageFromClientUI(ChatClient.java:85) 
at ClientConsole.accept(ClientConsole.java:77) 
at ClientConsole.main(ClientConsole.java:121)