Outputstream write() gets blocked using RXTX to communicate with HC-05 BT Module

Question

I've tried to solve the following Problem the last three days. I spend three days reading through various threads in many forums.

This is my problem: I try to send commands to a Bluetooth HC-05 device connected via a virtual Com-Port. In my case "COM4".

I used RXTX to establish a Connection to the Serial port. This works fine.

public static void main(String[] args) {
    portList = CommPortIdentifier.getPortIdentifiers();
    boolean portFound = false; 
    while (portList.hasMoreElements()) {
        portId = (CommPortIdentifier) portList.nextElement();
        if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
             if (portId.getName().equals("COM4")) {
                 portFound = true;
                SimpleRead reader = new SimpleRead();
            }
        }
    }
}

@SuppressWarnings("restriction")
public SimpleRead() {
    try {
        serialPort = (SerialPort) portId.open("SimpleReadApp", 2000);
    } catch (PortInUseException e) {System.out.println(e);}
    try {
        serialPort.setOutputBufferSize(15);
        serialPort.setEndOfInputChar((byte)'\n');
        inputStream = serialPort.getInputStream();
        outputStream = serialPort.getOutputStream();
    } catch (IOException e) {System.out.println(e);} catch (UnsupportedCommOperationException e)
        e.printStackTrace();
    }
    try {
        serialPort.addEventListener(this);
    } catch (TooManyListenersException e) {System.out.println(e);}

    serialPort.notifyOnDataAvailable(true);
    try {
        serialPort.setSerialPortParams(300,
            SerialPort.DATABITS_8,
            SerialPort.STOPBITS_1,
            SerialPort.PARITY_NONE);            
        serialPort.setFlowControlMode(SerialPort.FLOWCONTROL_NONE);
    } catch (UnsupportedCommOperationException e) {System.out.println(e);}
    serialPort.setRTS(true);
    serialPort.setDTR(true);
    serialPort.notifyOnDataAvailable(true);
    serialPort.setInputBufferSize(8192);
    serialPort.setOutputBufferSize(8192);

    writeThread = new Thread(new SerialWriter(outputStream));
    writeThread.start();

    readThread = new Thread(this);
    readThread.start();     
}

The Problem occures in the writer thread. When the writeTo() method of the ByteArrayOutputStream gets called the program hangs up without throwing an exception.

public class SerialWriter implements Runnable {
    OutputStream out;

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

    public void run() {
        try {
            Thread.sleep(500);
            while (true) {
                out.flush();
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                baos.write("AT\n".getBytes(Charset.forName("ASCII")));
                baos.writeTo(out); // <-- Here is my Problem. The program just
                                    // hangs up
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
    }
}

My OS is Windows 8.1 64bit.

I'm able to connect to the Bluetooth device with the console application hterm.

I appreciate any help or tip you can give me to solve this annoying problem!!