Sending a string via Bluetooth from a PC as client to a mobile as server

I need help by transferring a string from a PC to an Android mobile device via Bluetooth. The Android mobile device should act as a server and displays the string message on the screen of the device. The PC which is the client should send the string to the mobile device.

I want the server react on the extracted string (transferred via Bluetooth). That means that on one side the server always has to listen for new strings to arrive, but on the other side still has to be able to react on these messages (e.g. navigate from one menu to another).

I tried it by using BlueCove (2.1.1) as BluetoothStack (for which I add the jar from BlueCove as a library to both projects) in combination with an example for a server-client communication that I found here.

Updates:

Updated code from server thanks to user_CC using a RFComm connection for the server:

public class RFCommServer extends Thread{

//based on java.util.UUID
private static UUID MY_UUID = UUID.fromString("446118f0-8b1e-11e2-9e96-0800200c9a66");

// The local server socket
private BluetoothServerSocket mmServerSocket;

// based on android.bluetooth.BluetoothAdapter
private BluetoothAdapter mAdapter;
private BluetoothDevice remoteDevice;

private Activity activity;

public RFCommServer(Activity activity) {
    this.activity = activity;
}

public void run() {
    BluetoothSocket socket = null;
    mAdapter = BluetoothAdapter.getDefaultAdapter();        

    // Listen to the server socket if we're not connected
    while (true) {

        try {
            // Create a new listening server socket
            Log.d(this.getName(), ".....Initializing RFCOMM SERVER....");

            // MY_UUID is the UUID you want to use for communication
            mmServerSocket = mAdapter.listenUsingRfcommWithServiceRecord("MyService", MY_UUID);
            //mmServerSocket = mAdapter.listenUsingInsecureRfcommWithServiceRecord(NAME, MY_UUID); // you can also try using In Secure connection...

            // This is a blocking call and will only return on a
            // successful connection or an exception
            socket = mmServerSocket.accept();

        } catch (Exception e) {

        }

        try {
            Log.d(this.getName(), "Closing Server Socket.....");
            mmServerSocket.close();

            InputStream tmpIn = null;
            OutputStream tmpOut = null;

            // Get the BluetoothSocket input and output streams

            tmpIn = socket.getInputStream();
            tmpOut = socket.getOutputStream();

            DataInputStream mmInStream = new DataInputStream(tmpIn);
            DataOutputStream mmOutStream = new DataOutputStream(tmpOut);

            // here you can use the Input Stream to take the string from the client whoever is connecting
            //similarly use the output stream to send the data to the client

            RelativeLayout layout = (RelativeLayout) activity.findViewById(R.id.relativeLayout_Layout);
            TextView text = (TextView) layout.findViewById(R.id.textView_Text);

            text.setText(mmInStream.toString());
        } catch (Exception e) {
            //catch your exception here
        }
    }
}

Code of the SPP Client from here:

/**
* A simple SPP client that connects with an SPP server
*/
public class SampleSPPClient implements DiscoveryListener{

//object used for waiting
private static Object lock=new Object();

//vector containing the devices discovered
private static Vector vecDevices=new Vector();

private static String connectionURL=null;

public static void main(String[] args) throws IOException {

    SampleSPPClient client=new SampleSPPClient();

    //display local device address and name
    LocalDevice localDevice = LocalDevice.getLocalDevice();
    System.out.println("Address: "+localDevice.getBluetoothAddress());
    System.out.println("Name: "+localDevice.getFriendlyName());

    //find devices
    DiscoveryAgent agent = localDevice.getDiscoveryAgent();

    System.out.println("Starting device inquiry...");
    agent.startInquiry(DiscoveryAgent.GIAC, client);

    try {
        synchronized(lock){
            lock.wait();
        }
    }
    catch (InterruptedException e) {
        e.printStackTrace();
    }


    System.out.println("Device Inquiry Completed. ");

    //print all devices in vecDevices
    int deviceCount=vecDevices.size();

    if(deviceCount <= 0){
        System.out.println("No Devices Found .");
        System.exit(0);
    }
    else{
        //print bluetooth device addresses and names in the format [ No. address (name) ]
        System.out.println("Bluetooth Devices: ");
        for (int i = 0; i <deviceCount; i++) {
            RemoteDevice remoteDevice=(RemoteDevice)vecDevices.elementAt(i);
            System.out.println((i+1)+". "+remoteDevice.getBluetoothAddress()+" ("+remoteDevice.getFriendlyName(true)+")");
        }
    }

    System.out.print("Choose Device index: ");
    BufferedReader bReader=new BufferedReader(new InputStreamReader(System.in));

    String chosenIndex=bReader.readLine();
    int index=Integer.parseInt(chosenIndex.trim());

    //check for spp service
    RemoteDevice remoteDevice=(RemoteDevice)vecDevices.elementAt(index-1);
    UUID[] uuidSet = new UUID[1];
    uuidSet[0]=new UUID("446118f08b1e11e29e960800200c9a66", false);

    System.out.println("\nSearching for service...");
    agent.searchServices(null,uuidSet,remoteDevice,client);

    try {
        synchronized(lock){
            lock.wait();
        }
    }
    catch (InterruptedException e) {
        e.printStackTrace();
    }

    if(connectionURL==null){
        System.out.println("Device does not support Simple SPP Service.");
        System.exit(0);
    }

    //connect to the server and send a line of text
    StreamConnection streamConnection=(StreamConnection)Connector.open(connectionURL);

    //send string
    OutputStream outStream=streamConnection.openOutputStream();
    PrintWriter pWriter=new PrintWriter(new OutputStreamWriter(outStream));
    pWriter.write("Test String from SPP Client\r\n");
    pWriter.flush();


    //read response
    InputStream inStream=streamConnection.openInputStream();
    BufferedReader bReader2=new BufferedReader(new InputStreamReader(inStream));
    String lineRead=bReader2.readLine();
    System.out.println(lineRead);


}//main

//methods of DiscoveryListener
public void deviceDiscovered(RemoteDevice btDevice, DeviceClass cod) {
    //add the device to the vector
    if(!vecDevices.contains(btDevice)){
        vecDevices.addElement(btDevice);
    }
}

//implement this method since services are not being discovered
public void servicesDiscovered(int transID, ServiceRecord[] servRecord) {
    if(servRecord!=null && servRecord.length>0){
        connectionURL=servRecord[0].getConnectionURL(0,false);
    }
    synchronized(lock){
        lock.notify();
    }
}

//implement this method since services are not being discovered
public void serviceSearchCompleted(int transID, int respCode) {
    synchronized(lock){
        lock.notify();
    }
}


public void inquiryCompleted(int discType) {
    synchronized(lock){
        lock.notify();
    }

}//end method

}

For testing I use a Galaxy Nexus (GT-I9250) with the latest Android API.

Thanks to user_CC, the client and server now runs without an exception. But sadly the client is not able to connect to the server (see the screenshot below). It is because the connectionURL is never set (thus it jumps in here if(connectionURL==null) by default.

How can I change the client code, so that I actually can connect it with the server? I need a proper connectionURL in the following line:

StreamConnection streamConnection=(StreamConnection)Connector.open(connectionURL)

So far I only found out that I somehow need to get the ServiceRecord, sadly this is also not described in the example code from here.

You will need to use the RFComm APIS to make the communication work I have managed to define a class which is a Thread and will be acting as a server and listening for client connections. I have also placed some comments for you to understand.

    private class AcceptThread extends Thread {
    // The local server socket
    private BluetoothServerSocket mmServerSocket;

    public AcceptThread() {
    }

    public void run() {         
        BluetoothSocket socket = null;

                    BluetoothAdapter mAdapter = BluetoothAdapter.getDefaultAdapter();

        // Listen to the server socket if we're not connected
        while (true) {

            try {
                // Create a new listening server socket
                Log.d(TAG, ".....Initializing RFCOMM SERVER....");

                // MY_UUID is the UUID you want to use for communication
                mmServerSocket = mAdapter.listenUsingRfcommWithServiceRecord(NAME, MY_UUID);                    
                //mmServerSocket = mAdapter.listenUsingInsecureRfcommWithServiceRecord(NAME, MY_UUID);  you can also try using In Secure connection...

                // This is a blocking call and will only return on a
                // successful connection or an exception                    
                socket = mmServerSocket.accept();                   

            } catch (Exception e) {

            }

            try {
                Log.d(TAG, "Closing Server Socket.....";                    
                mmServerSocket.close();



                InputStream tmpIn = null;
                OutputStream tmpOut = null;

                // Get the BluetoothSocket input and output streams

                tmpIn = socket.getInputStream();
                tmpOut = socket.getOutputStream();


                mmInStream = new DataInputStream(tmpIn);
                mmOutStream = new DataOutputStream(tmpOut); 

                // here you can use the Input Stream to take the string from the client whoever is connecting
                //similarly use the output stream to send the data to the client
            } catch (Exception e) {
                //catch your exception here
            }

        }
    }

}

I hope this helps

For your another question:

Declaring javax.bluetooth.UUID on Client side (PC) UUID class should be from javax.bluetooth.UUID

   uuidSet2[0] = new UUID("446118f08b1e11e29e960800200c9a66", false);

Declaring java.util.UUID at Server Side (Android)

    UUID MY_UUID = UUID.fromString("446118f0-8b1e-11e2-9e96-0800200c9a66");