JSSC (Java Simple Serial Connector) is a lightweight Java library which built to write and read data from Serial Ports from a Java Application. For this tutorial we have used the latest version 2.9.2 of the JSSC library which we can get to date.

This code line initializing the COM port

serialPort = new SerialPort("COM1");  

This line is opening the COM Port connection

 serialPort.openPort();

Below code is setting the parameters for serial access.

   serialPort.setParams(SerialPort.BAUDRATE_9600,
                    SerialPort.DATABITS_8,
                    SerialPort.STOPBITS_1,
                    SerialPort.PARITY_NONE);

Below code managing the rate of data transmission via flow-control

serialPort.setFlowControlMode(SerialPort.FLOWCONTROL_RTSCTS_IN
                    | SerialPort.FLOWCONTROL_RTSCTS_OUT);

Once the application opened the port to receive data we can implement a listener for that. For this we are using an event reader as below

serialPort.addEventListener(new PortReader(), SerialPort.MASK_RXCHAR);

Same as reading data from serial port we can send data to the COM Port using below code lines

            String s = "Hello World \n";              
            serialPort.writeString(s);

Below is the event listener for the COM Port and once a data revised to the Serial Port this event listener will trigger.

private class PortReader implements SerialPortEventListener {

        @Override
        public void serialEvent(SerialPortEvent event) {
            if (event.isRXCHAR() && event.getEventValue() > 0) {
                try {
                    String receivedData = serialPort.readString(event.getEventValue());                    
                    System.out.println("Recvied Data : " + receivedData);
                } catch (SerialPortException ex) {
                    System.out.println("Error in receiving response from port: " + ex);
                }
            }
        }
 }

You can refer the full source code as below. You can use the same class to read/write to concurrent COM ports as well.

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package serialreader;
import jssc.*;

/**
 *
 * @author Sithara
 */
public class SerialDataReceiver implements Runnable {

    private SerialPort serialPort;

    private void initCOMPort() {
        serialPort = new SerialPort("COM1");
        try {
            serialPort.openPort();

            serialPort.setParams(SerialPort.BAUDRATE_9600,
                    SerialPort.DATABITS_8,
                    SerialPort.STOPBITS_1,
                    SerialPort.PARITY_NONE);

            serialPort.setFlowControlMode(SerialPort.FLOWCONTROL_RTSCTS_IN
                    | SerialPort.FLOWCONTROL_RTSCTS_OUT);

            serialPort.addEventListener(new PortReader(), SerialPort.MASK_RXCHAR);
            
            String s = "Hello World \n";  
            
            serialPort.writeString(s);
       
        } catch (SerialPortException ex) {   
            System.out.println("Error in writing data to port: " + ex);
        }
    }

    @Override
    public void run() {
        initCOMPort();
    }

    private class PortReader implements SerialPortEventListener {

        @Override
        public void serialEvent(SerialPortEvent event) {
            if (event.isRXCHAR() && event.getEventValue() > 0) {
                try {
                    String receivedData = serialPort.readString(event.getEventValue());                    
                    System.out.println("Recvied Data : " + receivedData);
                } catch (SerialPortException ex) {
                    System.out.println("Error in receiving response from port: " + ex);
                }
            }
        }
    }
}