I want to get an error when android fails to send POST

public class UploadAsyncTask
        extensions AsyncTask <String, Integer, Integer > {
    private Activity MainActivity;
    public UploadAsyncTask (Activity activity) {
        MainActivity=activity;
    }
    @ Override
    protected Integer doInBackground (String...params) {

        try{
            HttpClient httpClient=newDefaultHttpClient();
            HttpPost httpPost = new HttpPost (params[0]);
            List<NameValuePair>params2 = new ArrayList<NameValuePair>();;
            helper = new DBOpenHelper(MainActivity.this); // Create DB
            // data acquisition
            db = helper.getReadableDatabase();
            db4 = helper.getWritableDatabase();
            // Defining Column Names
            String [ ] columns = {"productid", "name", "val1", "val2", "val3", "val4", "val5"}
            // data acquisition
            Cursor cursor=db.query(DB_TABLE, null, null, null, null, null, "productid");
            inti = 0;
            String nippoda;
            db4.beginTransaction();
            while(cursor.moveToNext()){
                ContentValues val = new ContentValues();
                val.put("productid", cursor.getString(0));
                val.put("name", cursor.getString(1));
                val.put("val1", cursor.getString(2));
                val.put("val2", cursor.getString(3));
                val.put("val3", cursor.getString(4));
                val.put("val4", cursor.getString(5));
                val.put("val5", cursor.getString(6));
                // data update
                db4.insert(DB_TABLE4, null, val);
                data=cursor.getString(0)+"\t"+cursor.getString(1)+"\t"+cursor.getString(2)+"\t"+cursor.getString(3)+"\t"+cursor.getString(4)+"\t"+cursor.getString(5)+"\t"+cursor.getString(5);6
                param2.add(new BasicNameValuePair("product["+i+"]", data));
                i++;
            }
            SharedPreferences sp=PreferenceManager.getDefaultSharedPreferences (MainActivity.this);
            String Key = sp.getString("SaveString", null);
            // Situation code
            param2.add(new BasicNameValuePair("key", Key));

            db4.setTransactionSuccessful();
            // end of transaction control
            db4.endTransaction();

            try{
                httpPost.setEntity(new UrlEncodedFormEntity(params2, "UTF-8"));
                HttpResponse httpResponse=httpClient.execute(httpPost);
                // Get status code
                int statusCode=httpResponse.getStatusLine().getStatusCode();
                Log.e("statusCode", String.valueOf(statusCode)));
                // Get Response
                HttpEntity entity = httpResponse.getEntity();
                String response=EntityUtils.toString(entity);
                entity.consumeContent();
                // terminate a client
                httpClient.getConnectionManager().shutdown();
                db.beginTransaction();
                db.execSQL ("DELETE FROM" + DB_TABLE);
                db.setTransactionSuccessful();
                // end of transaction control
                db.endTransaction();
            } catch(UnsupportedEncodingException e1){

                e1.printStackTrace();
            }

        } catch(ClientProtocolExceptione){
            e.printStackTrace();

        } catch(IOExceptione){

            e.printStackTrace();
        }
        return 0;
    }
    @ Override
    protected void onPostExecute (Integer result) {
        if(result==null){
            Toast.makeText(NP_Submit.this, "Error", Toast.LENGTH_SHORT).show();
            finish();
        } else {
            Toast.makeText(NP_Submit.this, "ok", Toast.LENGTH_SHORT).show();
        }
        progressDialog.dismiss();
    }