Android : Refreshing a fragment inside a thread

I have an Android Application which is receveing info from a server. I am running a Thread to read the info and after that I want to update my fragment.

Here is the Thread:

public void receiveMessage(final Activity act){
    Thread t = new Thread(){
        public void run(){
            try{
                ServerSocket ss = new ServerSocket(4444);
                while(true){
                    Socket s = ss.accept();
                    ObjectInputStream dis = new ObjectInputStream(s.getInputStream());
                    final Mensagem m = (Mensagem) dis.readObject();
                    if(m != null){
                        ((MyApplication) act.getApplication()).setRoomHelper(m.getRoomHelper());
                        ((MyApplication) act.getApplication()).setIsNight(m.getIsNight());
                    }
                    Log.d("p", "RECEBI: " + m);

                    Handler handler = new Handler(Looper.getMainLooper());

                    handler.post(new Runnable() {

                        @Override
                        public void run() {
                            Log.d("b", "RUNNN");
                            Toast.makeText(act, "JANELA: " + m.getRoomHelper().isWindow() + " e LUZ: "
                                    + m.getRoomHelper().isLight(), Toast.LENGTH_LONG).show();
                        }
                    });
                    dis.close();
                    s.close();
                    Fragment fragment = new Room();
                    FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
                    fragmentManager.beginTransaction()
                            .replace(R.id.container, fragment)
                            .commit();
                }
            }
            catch(IOException e){

            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
    };
    t.start();
}

I want to update my fragment beucase this line here:

                        ((MyApplication) act.getApplication()).setRoomHelper(m.getRoomHelper());

receives a lot of new info which and I need to updated it with the info I receive. The problem is I am getting:

12-13 23:24:48.133    5583-5866/com.example.rui.smarthome W/dalvikvm﹕ threadid=13: thread exiting with uncaught exception (group=0x4163ad40)
12-13 23:24:48.134    5583-5866/com.example.rui.smarthome E/AndroidRuntime﹕ FATAL EXCEPTION: Thread-42438
    Process: com.example.rui.smarthome, PID: 5583
    java.lang.NullPointerException
            at com.example.rui.smarthome.Room$6.run(Room.java:622)
12-13 23:24:48.188    5583-5583/com.example.rui.smarthome D/AndroidRuntime﹕ Shutting down VM
12-13 23:24:48.195    5583-5583/com.example.rui.smarthome W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x4163ad40)
12-13 23:24:48.195    5583-5583/com.example.rui.smarthome I/Process﹕ Sending signal. PID: 5583 SIG: 9

The error line is this one:

FragmentManager fragmentManager = getActivity().getSupportFragmentManager();

So, since I am thinking I can't use that in here, which other options, not changing a lot of the code do I have?

I was thinking about a solution using a boolean, iniatialized outside of the thread and setting it to true inside it. The thing is it needs be declared final, so I can't change it inside the thread.