Serial Communication using RxTx library in Java(Windows)

In this post I expect to explain how to use Java RxTx library to carry out a two way serial communication with an Arduino. On downloading and installing Java RxTx serial communication library please refer this link http://duvindu92.blogspot.com/2013/07/installing-java-rxtx-library-for-serial.html.

In this sample code first a string is sent by the Arduino requesting the name of the user. Once the user types in the name, it is sent back to the Arduino through the serial port and Arduino returns a welcome message, "Hello"+ <yourName>. So lets begin

The JAVA Code

import java.io.BufferedReader;                    //BufferedReader makes reading operation efficient

import java.io.InputStreamReader;         //InputStreamReader decodes a stream of bytes into a character set

import java.io.OutputStream;          //writes stream of bytes into serial port

import gnu.io.CommPortIdentifier;           

import gnu.io.SerialPort;

import gnu.io.SerialPortEvent;            //deals with possible events in serial port (eg: data received)

import gnu.io.SerialPortEventListener; //listens to the a possible event on serial port and notifies when it does

import java.util.Enumeration;

import gnu.io.PortInUseException;           //all the exceptions.Never mind them for now

import java.io.IOException;

import gnu.io.UnsupportedCommOperationException;

import java.util.TooManyListenersException;

import java.util.Scanner;                                   //to get user input of name

public class SerialTest implements SerialPortEventListener {        

   

    private SerialPort serialPort ;         //defining serial port object

    private CommPortIdentifier portId  = null;       //my COM port

    private static final int TIME_OUT = 2000;    //time in milliseconds

    private static final int BAUD_RATE = 9600; //baud rate to 9600bps

    private BufferedReader input;               //declaring my input buffer

    private OutputStream output;                //declaring output stream

    private String name;        //user input name string

    Scanner inputName;          //user input name

    //method initialize

    private void initialize(){

        CommPortIdentifier ports = null;      //to browse through each port identified

        Enumeration portEnum = CommPortIdentifier.getPortIdentifiers(); //store all available ports

        while(portEnum.hasMoreElements()){  //browse through available ports

                ports = (CommPortIdentifier)portEnum.nextElement();

             //following line checks whether there is the port i am looking for and whether it is serial

               if(ports.getPortType() == CommPortIdentifier.PORT_SERIAL&&ports.getName().equals("COM6")){ 

                System.out.println("COM port found:COM6");

                portId = ports;                  //initialize my port

                break;                                                                                     }

           

            }

       //if serial port am looking for is not found

        if(portId==null){

            System.out.println("COM port not found");

            System.exit(1);

        }

        

                            }

    

    //end of initialize method

    

    //connect method

   

    private void portConnect(){

        //connect to port

        try{

         serialPort = (SerialPort)portId.open(this.getClass().getName(),TIME_OUT);   //down cast the comm port to serial port

                                                                                     //give the name of the application

                                                                                     //time to wait

        System.out.println("Port open succesful: COM6"); 

        

        //set serial port parameters

serialPort.setSerialPortParams(BAUD_RATE,SerialPort.DATABITS_8,SerialPort.STOPBITS_1,SerialPort.PARITY_NONE);

        

        

        }

        catch(PortInUseException e){

            System.out.println("Port already in use");

            System.exit(1);

        }

        catch(NullPointerException e2){

            System.out.println("COM port maybe disconnected");

        }

        catch(UnsupportedCommOperationException e3){

            System.out.println(e3.toString());

        }

       

        //input and output channels

        try{

      //defining reader and output stream

       input = new BufferedReader(new InputStreamReader(serialPort.getInputStream()));

        output =  serialPort.getOutputStream();

        //adding listeners to input and output streams

        serialPort.addEventListener(this);

        serialPort.notifyOnDataAvailable(true);

        serialPort.notifyOnOutputEmpty(true);

        }

        catch(Exception e){

            System.out.println(e.toString());

                            }

        

    }

    //end of portConncet method

    

    //readWrite method

   

    public void serialEvent(SerialPortEvent evt) { 

   

       if (evt.getEventType() == SerialPortEvent.DATA_AVAILABLE) { //if data available on serial port

try {

String inputLine=input.readLine();

System.out.println(inputLine);

                                inputName = new Scanner(System.in); //get user name

                                name = inputName.nextLine();

                                name = name + '\n';

                                System.out.printf("%s",name);

                                output.write(name.getBytes());     //sends the user name

} catch (Exception e) {

System.err.println(e.toString());

}

}

       

    }

    //end of serialEvent method

    

    //closePort method

    private void close(){

        if(serialPort!=null){

            serialPort.close(); //close serial port

        }

        input = null;        //close input and output streams

        output = null;

    }

    //main method

    public static void main(String[] args) {

        SerialTest myTest = new SerialTest();  //creates an object of the class

        myTest.initialize();

        myTest.portConnect();

       System.out.println("Started");

       while(1>0);       //wait till any activity

        

       

                                            }

//end of main method

// end of  SerialTest class

}

Arduino Code

boolean stringComplete = false;

String inputString = "";

int led=13;

void setup(){

Serial.begin(9600);

pinMode(led,OUTPUT);

Serial.println("Hi, What's Your Name");

                  }

void serialEvent() {

  while (Serial.available()) {

    

    char inChar = (char)Serial.read(); 

    inputString += inChar;

    if (inChar == '\n') {

      stringComplete = true;

                                    }

   Serial.flush();

    //end of while()

                                     }

    //end of serialEvent

                    }

void loop(){

       if(stringComplete){

             digitalWrite(led,HIGH);

             String name = "Hello "+ inputString; 

             inputString = "";

             Serial.println(name);

             stringComplete = false;

                                 }

             }

For more information on use of RxTx library in java you can refer the following links

1. Reading Serial Data from Arduino : http://playground.arduino.cc/Interfacing/Java
2. Two way communication using Java RxTx with Arduino :
            http://henrypoon.wordpress.com/2011/01/01/serial-communication-in-java-with-example-program/

3. Java serial communication: http://en.wikibooks.org/wiki/Serial_Programming/Serial_Java