Duvidas com relação a porta serial

Estou tendo dificuldades em trabalhar com a porta serial, meu problema é o seguinte:

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Enumeration;
import java.util.TooManyListenersException;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.comm.CommPortIdentifier;
import javax.comm.PortInUseException;
import javax.comm.SerialPort;
import javax.comm.SerialPortEvent;
import javax.comm.SerialPortEventListener;

import javax.swing.JOptionPane;

public class MainClass implements Runnable, SerialPortEventListener {
  static CommPortIdentifier portId;

  static Enumeration portList;

  InputStream inputStream;

  SerialPort serialPort;

  Thread readThread;
  int i = 0;
  
  public String Dadoslidos;
  private Connection conn;
  private PreparedStatement prepared;
  private String sSql;

  Frame frame = new Frame();
  
  public static void main(String[] args) {
      Frame frame = new Frame();
      
      
      portList = CommPortIdentifier.getPortIdentifiers();
      while (portList.hasMoreElements()) {
        portId = (CommPortIdentifier) portList.nextElement();
        if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
           if (portId.getName().equals("COM1")) {
            MainClass reader = new MainClass();
           }
        }
      }
  }

  public MainClass() {
    try {
      serialPort = (SerialPort) portId.open("MainClassApp", 2000);
    } catch (PortInUseException e) {
        JOptionPane.showMessageDialog(null,"A porta já está sendo usada! " + e);
    }
    try {
      inputStream = serialPort.getInputStream();
    } catch (IOException e) {  
        JOptionPane.showMessageDialog(null,"Falha ou Interrupção de E / S! " + e);
    }
    catch (Exception e) {
      JOptionPane.showMessageDialog(null,"Erro.STATUS: " + e);
      System.exit(1);
    }
    try {
      serialPort.addEventListener(this);
    } catch (TooManyListenersException e) {
    }
    catch (Exception e) {
      JOptionPane.showMessageDialog(null,"Erro ao criar listener. STATUS: " + e);
      System.exit(1);
    }
    serialPort.notifyOnDataAvailable(true);
    try {
      serialPort.setSerialPortParams(4800, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
    } catch (Exception e) {
        JOptionPane.showMessageDialog(null,"Erro ao abrir a porta! STATUS: " + e );
    }
    readThread = new Thread(this);
    readThread.start();
  }

  public void run() {
    try {
      Thread.sleep(500);
    } catch (InterruptedException e) {
        JOptionPane.showMessageDialog(null,"Thread Interrompida: " + e );
    }
  }

  public void serialEvent(SerialPortEvent event) {
    switch (event.getEventType()) {
    case SerialPortEvent.BI:
    case SerialPortEvent.OE:
    case SerialPortEvent.FE:
    case SerialPortEvent.PE:
    case SerialPortEvent.CD:
    case SerialPortEvent.CTS:
    case SerialPortEvent.DSR:
    case SerialPortEvent.RI:
        break;
    case SerialPortEvent.OUTPUT_BUFFER_EMPTY:
        JOptionPane.showMessageDialog(null, "Passou");
        AbrirConexao();
        sSql = "Update Usu_T001Med Set Usu_QtdMed = " + Dadoslidos + " Where Usu_NumSer = '441'";
        try {
            prepared = conn.prepareStatement(sSql);
            prepared.executeUpdate();
            prepared.close();
        } catch (SQLException e) {
            JOptionPane.showMessageDialog(null, "Problemas ao Gravar Dados no Banco! " + e);
        }
        try {
            prepared.close();
            conn.close();
        } catch (SQLException ex) {
            Logger.getLogger(MainClass.class.getName()).log(Level.SEVERE, null, ex);
        }         
      break;
    
    case SerialPortEvent.DATA_AVAILABLE:
      byte[] readBuffer = new byte[20];

      try {
        while (inputStream.available() > 0) {
          int numBytes = inputStream.read(readBuffer);
          Dadoslidos = new String(readBuffer);
//          i ++;
//          frame.teste.setText(Integer.toString(i));
          Dadoslidos = Dadoslidos.replaceAll("\\D", "");
          if(!Dadoslidos.equals("")){
              frame.sQtdMed.setText(Dadoslidos);
          }
        }
        if(inputStream.available() == 0) {
            i = i +1;
          frame.teste.setText(Integer.toString(i));
        }else{
           frame.teste.setText("teste"); 
        }
      }
      catch (IOException e) {
      }
      break;
    }
    Object obj;
        try {
            obj = inputStream.available();
            frame.sEvento.setText(obj.toString());
        } catch (IOException ex) {
            Logger.getLogger(MainClass.class.getName()).log(Level.SEVERE, null, ex);
        }

  }
  
  public void AbrirConexao(){
    try{
        Class.forName("oracle.jdbc.driver.OracleDriver");
        conn = DriverManager.getConnection("jdbc:oracle:thin:@DELL:1521:dbprod", "sapiens_novo", "sapiens_novo");
    }
    catch(ClassNotFoundException erro)
    {
        JOptionPane.showMessageDialog(null,"Driver JDBC_ORACLE não encontrado! \n" + erro);
    }
    catch(SQLException erro)
    {
        JOptionPane.showMessageDialog(null,"Problemas na conexão com o banco de dados. \n"  + erro);
    }       
  }
}