Why my android app force close when i try to get web page using the httpclient?

Question

I'm using this code,

class RequestTask extends AsyncTask<String, String, String>{

@Override
// username, password, message, mobile
protected String doInBackground(String... url) {
    // constants
    int timeoutSocket = 5000;
    int timeoutConnection = 5000;

    HttpParams httpParameters = new BasicHttpParams();
    HttpConnectionParams.setConnectionTimeout(httpParameters, timeoutConnection);
    HttpConnectionParams.setSoTimeout(httpParameters, timeoutSocket);
    HttpClient client = new DefaultHttpClient(httpParameters);

    HttpGet httpget = new HttpGet(url[0]);

    try {
        HttpResponse getResponse = client.execute(httpget);
        final int statusCode = getResponse.getStatusLine().getStatusCode();

        if(statusCode != HttpStatus.SC_OK) {
            Log.w("MyApp", "Download Error: " + statusCode + "| for URL: " + url);
            return null;
        }

        String line = "";
        StringBuilder total = new StringBuilder();

        HttpEntity getResponseEntity = getResponse.getEntity();

        BufferedReader reader = new BufferedReader(new InputStreamReader(getResponseEntity.getContent()));  

        while((line = reader.readLine()) != null) {
            total.append(line);
        }

        line = total.toString();
        return line;
    } catch (Exception e) {
        Log.w("MyApp", "Download Exception : " + e.toString());
    }
    return null;
}

@Override
protected void onPostExecute(String result) {
    // do something with result
}
}

I call the execute method in the onCreate method. And when i tried to start the app, it's always force close. I tried to narrow the error, and i found that the HttpResponse getResponse = client.execute(httpget); that caused the error. I dont know why this didnt work for me? any help?