How to convert String to Hex and Hex to String?

I made a simple program to send and receive data to a serial port in java. I am connecting a serial port device with feedback check (Rx to Tx). It works great. but I can not send and receive hexadecimal data to the serial port and restore the serial port. My device uses the FT232BL chip. There is also some kind of dll or other library needed to send and receive hexadecimal data to the serial port device. my code is below.

enter code here
package x.rayimagecapture;

import gnu.io.CommPort;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class TwoWaySerialComm extends JPanel implements ActionListener {

    OutputStream out;
    private javax.swing.JButton btn;
    private javax.swing.JScrollPane jScrollPane1;
    public static javax.swing.JLabel jLabel1;
    public static javax.swing.JTextField textField;
    public static boolean flag = false;
    public static int count = 50;
//    TimerWindow tmr=new TimerWindow();
    public static Timer tmr = new Timer(1000, new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
                        count++;
            jLabel1.setText("" + count);
        }
    });

    public TwoWaySerialComm() {
        super();
        textField = new javax.swing.JTextField();
        btn = new javax.swing.JButton();
        jScrollPane1 = new javax.swing.JScrollPane();
        jLabel1 = new javax.swing.JLabel();
        textField.setText(""); // NOI18N
//        tmr.setDelay(0);

        btn.setFont(new java.awt.Font("Tahoma", 0, 12)); // NOI18N
        btn.setText("Send"); // NOI18N
        btn.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                serialwrite();
            }
        });

//        textArea.setColumns(20);
//        textArea.setRows(20);
//        textArea.setTabSize(0);
        jScrollPane1.setViewportView(jLabel1);

        javax.swing.GroupLayout panelLayout = new javax.swing.GroupLayout(this);
        this.setLayout(panelLayout);
        panelLayout.setHorizontalGroup(
                panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(panelLayout.createSequentialGroup()
                .addComponent(textField, javax.swing.GroupLayout.PREFERRED_SIZE, 300, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(btn, javax.swing.GroupLayout.DEFAULT_SIZE, 84, Short.MAX_VALUE)
                .addContainerGap())
                .addComponent(jScrollPane1));
        panelLayout.setVerticalGroup(
                panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(panelLayout.createSequentialGroup()
                .addGroup(panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(textField, javax.swing.GroupLayout.PREFERRED_SIZE, 47, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(btn, javax.swing.GroupLayout.PREFERRED_SIZE, 37, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 218, Short.MAX_VALUE)));
    }

    void connect(String portName) throws Exception {
        CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier(portName);
        if (portIdentifier.isCurrentlyOwned()) {
            System.out.println("Error: Port is currently in use");
        } else {
            CommPort commPort = portIdentifier.open(this.getClass().getName(), 2000);

            if (commPort instanceof SerialPort) {
                SerialPort serialPort = (SerialPort) commPort;
                serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
                serialPort.setFlowControlMode(SerialPort.FLOWCONTROL_NONE);
                InputStream in = serialPort.getInputStream();
                out = serialPort.getOutputStream();

                (new Thread(new SerialReader(in))).start();
//                (new Thread(new SerialWriter(out))).start();

            } else {
                System.out.println("Error: Only serial ports are handled by this example.");
            }
        }
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        serialwrite();
    }

    public void serialwrite() {
        try {
            this.out.write(textField.getText().toString().getBytes());
            count = 00;
//            tmr.start();
            tmr.start();
            this.out.flush();
        } catch (IOException ex) {
            Logger.getLogger(TwoWaySerialComm.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    /**
     *
     */
    public static class SerialReader implements Runnable {

        InputStream in;

        public SerialReader(InputStream in) {
            this.in = in;
        }

        public void run() {
            byte[] buffer = new byte[1024];
            int len = -1;
            try {
                while ((len = this.in.read(buffer)) != -1) {
//                    textArea.append(" " + new String(buffer, 0, len));
                    String str = new String(buffer, 0, len);
                    System.out.print(str);
                    if (!str.isEmpty()) {
//                        tmr.stop();
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     *
     */
    public static class SerialWriter implements Runnable {

        OutputStream out;

        public SerialWriter(OutputStream out) {
            this.out = out;
        }

        public void run() {
            try {
                int c = 0;
                while ((c = System.in.read()) != -1) {
//                    this.out.write(c);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        TwoWaySerialComm tws = new TwoWaySerialComm();
        JFrame frame = new JFrame();
        frame.setSize(400, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(tws);
        try {
            tws.connect("COM11");
        } catch (Exception ex) {
            Logger.getLogger(TwoWaySerialComm.class.getName()).log(Level.SEVERE, null, ex);
        }
        frame.setVisible(true);
    }
}