How to send command to serial port (JAVA + RXTX)

I have a problem with sending data input to a weight balance. I need to send a ESC P CR LF command. I use the RXTX lib. I dont know why it does not work.

Here is the code:

public static class SerialWriter implements Runnable {
    OutputStream out;

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

    public void run () {
        try {                
            while (true) {
               this.out.write(new byte[]{0x1B, 0x50, 0x0D, 0x0A});
                Thread.sleep(1000);
            }                
        } catch ( IOException | InterruptedException e ) {
            e.printStackTrace();
        }            
    }
}

I tried with flush but nothing happened.

I attached the full (modified) code below.

package model;

import gnu.io.CommPort;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;

import java.io.FileDescriptor;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class FirstSteps {
    public FirstSteps() {
        super();
    }

    void connect (String portName) throws Exception {
        CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier(portName);
        if (portIdentifier.isCurrentlyOwned()) {
            System.out.println("Error: Port is currently in use");
        } else {
            System.out.println("Connect 1/2");
            CommPort commPort = portIdentifier.open(this.getClass().getName(),6000);
            if (commPort instanceof SerialPort) {
                System.out.println("Connect 2/2");
                SerialPort serialPort = (SerialPort) commPort;
                System.out.println("BaudRate: " + serialPort.getBaudRate());
                System.out.println("DataBIts: " + serialPort.getDataBits());
                System.out.println("StopBits: " + serialPort.getStopBits());
                System.out.println("Parity: " + serialPort.getParity());
                System.out.println("FlowControl: " + serialPort.getFlowControlMode());
                serialPort.setSerialPortParams(4800,SerialPort.DATABITS_8,SerialPort.STOPBITS_1,SerialPort.PARITY_ODD);
            serialPort.setFlowControlMode(SerialPort.FLOWCONTROL_RTSCTS_IN);
                System.out.println("BaudRate: " + serialPort.getBaudRate());
                System.out.println("DataBIts: " + serialPort.getDataBits());
                System.out.println("StopBits: " + serialPort.getStopBits());
                System.out.println("Parity: " + serialPort.getParity());
                System.out.println("FlowControl: " + serialPort.getFlowControlMode());
                InputStream in = serialPort.getInputStream();
                OutputStream 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.");
            }
        }     
    }

    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) {
                    //System.out.println("Received a signal.");
                    System.out.print(new String(buffer,0,len));
                }
            } catch ( IOException e ) {
                e.printStackTrace();
            }            
        }
    }

    public static class SerialWriter implements Runnable {
        OutputStream out;

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

        public void run() {
            try {
                byte[] array = {0x1B, 0x50, 0x0D, 0x0A};
                while (true) {
                    this.out.write(new byte[]{0x1B, 0x50, 0x0D, 0x0A});
                    this.out.flush();
                    Thread.sleep(1000);  
                }                
            } catch ( IOException | InterruptedException e ) {
                e.printStackTrace();
            }            
        }
    }

    public static void main(String[] args) {
        try {
            (new FirstSteps()).connect("COM7");
        } catch ( Exception e ) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

Based on the provided code the only suggestion I could give is to try flushing the stream (out.flush()) after putting data in it.

Other than that - I'd need to see the code that gets the output stream.