Why am I losing bluetooth client/server connection?

Question

I am trying to connect from a desktop application (written in Java) to a Android application through Bluetooth.
For the desktop application I am using BlueCove API.
When I start the server (desktop application) and I start the Android application, the connection works fine. (i.e. The client sends a "Hello World" and the server prints it in the console). But when I leave the application (by pressing Back or Home button) and return back to it, the socket connection seems to be lost.

How can you check if a Bluetooth socket is already connected?
I would like to check the connection of the socket to not having connecting again.

What should I write (if it is the case) in the onPause, onResume methods?
I suppose that in the onDestroy method I should close the socket.

Here is the source code of the client server:
Server
Client

I also tried using IntentFilter to check for the state of the connection, but it didn't work.

@Override
    public void onCreate(Bundle savedInstanceState) {
             // ..... 

        IntentFilter filter1 = new IntentFilter(BluetoothDevice.ACTION_ACL_CONNECTED);
        IntentFilter filter2 = new IntentFilter(BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED);
        IntentFilter filter3 = new IntentFilter(BluetoothDevice.ACTION_ACL_DISCONNECTED);
        this.registerReceiver(mReceiver, filter1);
        this.registerReceiver(mReceiver, filter2);
        this.registerReceiver(mReceiver, filter3);

}

//The BroadcastReceiver that listens for bluetooth broadcasts
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);

        if (BluetoothDevice.ACTION_FOUND.equals(action)) {
           //Device found
            Toast.makeText(BluetoothClient.this, "Device not found", 2).show();
        }
        else if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {
          //Device is now connected
            Toast.makeText(BluetoothClient.this, "Device connected", 2).show();
        }
        else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
          //Done searching
            Toast.makeText(BluetoothClient.this, "Done searching", 2).show();
        }
        else if (BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED.equals(action)) {
            //Device is about to disconnect
            Toast.makeText(BluetoothClient.this, "Device about to connect", 2).show();
        }
        else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(action)) {
         //Device has disconnected
            Toast.makeText(BluetoothClient.this, "Device disconnected", 2).show();
        }           
    }
};

Answer 1

Server
Client

I have modified the 2 source code files.
Now it should work fine. There are some small bugs regarding if the BT is not opened before entering the mobile app (it get stuck too much in a while) and for those who want to use this client/server you should take a look at onPause(), onResume(), onDestroy() functions.

The problem was that I did not use the socket correctly.

I hope that it will be useful for those who want to implement such an application with BT.