null pointer exception during android listview refresh

i want to update my list view after downloading complete but it gives me Nullpointer Exception my code is as per under

try {
                    URL url = new URL(GlobalVariable.Getstr());
                    HttpURLConnection c = (HttpURLConnection) url.openConnection();
                    c.setRequestMethod("GET");
                    c.setDoOutput(true);
                    c.connect();
                       int lenghtOfFile = c.getContentLength();
                       Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);
                    String PATH = Environment.getExternalStorageDirectory()
                            + "/download/";
                    Log.v(LOG_TAG, "PATH: " + PATH);
                    File file = new File(PATH);
                    file.mkdirs();
                    // String fileName = "workTest.mp3";
                    String fileName = GlobalVariable.Getstrpath().toString();
                    File outputFile = new File(file, fileName);
                    FileOutputStream fos = new FileOutputStream(outputFile);
                    InputStream is = c.getInputStream();
                    byte[] buffer = new byte[1024];
//                  int len1 = 0;
                     long total = 0;
//                  while ((len1 = is.read(buffer)) != -1) {
//                      total += len1;
//                      publishProgress(""+(int)((total*100)/lenghtOfFile));
//                      fos.write(buffer, 0, len1);
//
                     while ((count = is.read(buffer)) != -1) {
                            total += count;
                            publishProgress(""+(int)((total*100)/lenghtOfFile));
                            fos.write(buffer, 0, len1);
                    }
                    fos.close();
                    is.close();
//                  ArrayAdapter aa=new ArrayAdapter(FindFilesByType.this, android.R.layout.test_list_item,Ringtones);
//                  aa.setNotifyOnChange(true);
//                  lv1.setAdapter(aa);
                    try{
                        ((ArrayAdapter) lv1.getAdapter()).notifyDataSetChanged();
                //      adapter.notifyDataSetChanged();
                    }
                    catch (Exception e) {
                        Log.i(LOG_TAG, "Error: " + e.toString());
                    }

i am getting the

04-28 15:56:17.198: INFO/app(624): Error: java.lang.NullPointerException

what is wrong i am doing?

thanks in advance