About controlling led using java rxtx

Question

I wrote a simple led control program and uploaded to Arduino, it works well when I use the "serial monitor" to send the control command to Arduino. While, I try to write a java program on ubuntu to send the command. I can see the RX lights flashing when I run my java program, but it seems Arduino did not recognize the commands.

I post my codes here. Wish any one could kindly help me.

import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Enumeration;

import gnu.io.* ;     // rxtx serial port driver

public class SerialTest {
    static Enumeration          portList;
    static CommPortIdentifier   portId;
    static SerialPort           serialPort;
    static OutputStream         outputStream;
    static boolean              outputBufferEmptyFlag = false;

    public static void main( String[] args) {
        boolean portFound = false;
        String  defaultPort = "/dev/ttyACM0";

        if (args.length > 0) {
            defaultPort = args[0];
        }

        portList = CommPortIdentifier.getPortIdentifiers();

        while(portList.hasMoreElements()) {
            portId = (CommPortIdentifier) portList.nextElement();

            if(portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {

                if(portId.getName().equals(defaultPort)) {
                    System.out.println("Found port " + defaultPort);

                    portFound = true;

                    try {
                        serialPort = (SerialPort) portId.open("SerialTest", 2000);
                    } catch (PortInUseException e) {
                        System.out.println("Port in use.");
                        continue;
                    } 

                    try {
                        serialPort.setSerialPortParams(9600, 
                                        SerialPort.DATABITS_8, 
                                        SerialPort.STOPBITS_1, 
                                        SerialPort.PARITY_NONE);
                    } catch (UnsupportedCommOperationException e) {}

                    try {
                        outputStream = serialPort.getOutputStream();
                        outputStream.write("cccc".getBytes());
                    } catch (IOException e) {}

                    serialPort.close();
                    System.exit(1);
                } 
            } 
        }
    }
}