This class implement some simple methods to write datas on a serial bus. This implementation used the RXTXComm library (http://rxtx.qbang.org/wiki/index.php/Download). This example is configured to use this `/dev/ttyACM0` port (may require some tweaks). Typically you could used this code to send/write some datas to an Arduino.

SerialArduino.java

package fr.blckshrk.core.utils.serial;

import gnu.io.CommPortIdentifier;
import gnu.io.NoSuchPortException;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;

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

public class SerialArduino implements SerialPortEventListener {

	SerialPort serialPort;

	/** Buffered input stream from the port */
	private InputStream input;

	/** The output stream to the port */
	private OutputStream output;

	/** Milliseconds to block while waiting for port open */
	private static final int TIME_OUT = 2000;

	/** Default bits per second for COM port. */
	private static final int DATA_RATE = 115200;

	private String inputBuffer = "";

	/**
	 * 
	 */
	public boolean initialize() {
		System.setProperty("gnu.io.rxtx.SerialPorts", "/dev/ttyACM0");

		CommPortIdentifier portId = null;
		try {
			portId = CommPortIdentifier.getPortIdentifier("/dev/ttyACM0");
		} catch (NoSuchPortException e1) {
			System.err.println(e1.getMessage());
			return false;
		}

		if (portId == null) {
			System.err.println("Could not find COM port.");
			return false;
		}

		try {
			// open serial port, and use class name for the appName.
			serialPort = (SerialPort) portId.open(this.getClass().getName(), TIME_OUT);

			// set port parameters
			serialPort.setSerialPortParams(DATA_RATE,
					SerialPort.DATABITS_8,
					SerialPort.STOPBITS_1,
					SerialPort.PARITY_NONE);
			
			//waiting for opening
			Thread.sleep(2000);

			// open the streams
			input = serialPort.getInputStream();
			output = serialPort.getOutputStream();

			// add event listeners
			serialPort.addEventListener(this);
			serialPort.notifyOnDataAvailable(true);
			
			return true;

		} catch (Exception e) {
			System.err.println(e.getMessage());
		}
		
		return false;
	}

	/**
	 * This should be called when you stop using the port.
	 * This will prevent port locking on platforms like Linux.
	 */
	public synchronized void close() {
		if (serialPort != null) {
			serialPort.removeEventListener();
			serialPort.close();
		}
	}

	/**
	 * This Method can be called to print a String
	 * to the serial connection
	 * @param msg
	 */
	public synchronized void write(String msg){
		try {
			output.write(msg.getBytes()); //write it to the serial
			output.flush(); 			//refresh the serial
		} catch (Exception e) {
			System.err.println(e.getMessage());
		}
	}
	
	/**
	 * This Method can be called to print a String
	 * to the serial connection
	 * @param msg
	 */
	public synchronized void writeln(String msg){
		write(msg + '\n');
	}
	
	/**
	 * This method is called to read one byte
	 * @return
	 */
	public synchronized int read() {
		int c = 0;
		
		try {
			c = input.read();
		} catch (IOException e) {
			System.err.println(e.getMessage());
		}
		
		return c;
	}
	
	/**
	 * This method is called to read a line terminated by '\n' or '\r\n'
	 * @return
	 */
	public synchronized String readln() {
		String str = "";
		int c = -1;
		
		while ((c = read()) != '\n' && c != -1) {
			if (c == '\r') {
				continue;
			}
			str += (char) c;
		}
		
		return str;
	}

	/**
	 * This Method is called when a command is recieved
	 * and needs to be encoded
	 * @param com
	 */
	private synchronized void encodeCommand(String com){
		//checks if the String starts with s for set
		if (com.indexOf("s:") == 0) {
			String id = com.substring(com.indexOf("s:") + 2, com.indexOf(","));	//remove the s, and store the "p1"
			String value = com.substring(com.indexOf(",") + 1, com.length());	//store everything after the ","
			
			if (id.equals("p1") && !value.equals("")) {//if it's my poti1 and it sends a value
				String myValue = "s:s1," + value;	//set the value to my servo1
				writeln(myValue);					//and send it via the serial
			} else {
				System.err.println("Not correct values");
			}
		}
	}

	/**
	 * This Method is called when Serialdata is recieved
	 */
	@Override
	public synchronized void serialEvent (SerialPortEvent oEvent) {
		if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
			try {
				int available = input.available();
				for (int i = 0; i < available; i++) {	//read all incoming characters
					int receivedVal = input.read();		//store it into an int (because of the input.read method
					
					if (receivedVal != 10 && receivedVal != 13) {//if the character is not a new line "\n" and not a carriage return
						inputBuffer += (char)receivedVal;		//store the new character into a buffer
					} else if (receivedVal == 10) {				//if it's a new line character
						encodeCommand(inputBuffer);				//call the method to encode the recieved command
						inputBuffer = "";						//clear the buffer
					}
				}
			} catch (Exception e) {
				System.err.println(e.getMessage());
			}
		}
	}

	/**
	 * For debugging only
	 * @param args
	 * @throws Exception
	 */
	public static void main(String[] args) throws Exception {
		SerialArduino serial = new SerialArduino();
		if (!serial.initialize()) {
			System.err.println("Initialization failed.");
			System.exit(-1);
		}
		
		System.out.println("Started");
		

		for (int i = 0; i <= 255; i++) {
			serial.writeln(i + " " + i + " " + i);
			System.out.println("RGB: " + i + " " + i + " " + i);

			Thread.sleep(10);
		}

		for (int i = 255; i >= 0; i--) {
			serial.writeln(i + " " + i + " " + i);
			System.out.println("RGB: " + i + " " + i + " " + i);

			Thread.sleep(10);
		}
		
		for (int i = 0; i <= 255; i++) {
			serial.writeln(i + " " + (255 - i) + " 0");
			System.out.println("RGB: " + i + " " + (255 - i) + " 0");

			Thread.sleep(10);
		}

		serial.close();
	}
}