问获取json对象的NullPointerException

EN

public boolean fileData(String guid, String photoName) {
    Toast.makeText(getApplicationContext(), photoName, Toast.LENGTH_LONG).show();

    JSONObject json = userFunctions.uploadFileData(guid, photoName);

    try {
        if(Integer.parseInt(json.getString("success")) != 1) {
            Toast.makeText(getApplicationContext(), json.getInt("error_msg"), Toast.LENGTH_LONG).show();
            //register_error.setText(json.getString("error_msg"));
            return false;
        }
    } catch (NumberFormatException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return true;
}

public JSONObject uploadFileData(String uid, String photoName) {
    List<NameValuePair> params = new ArrayList<NameValuePair>();
    params.add(new BasicNameValuePair("tag", file_tag));
    params.add(new BasicNameValuePair("uid", uid));
    params.add(new BasicNameValuePair("photoName", photoName));
    JSONObject json = jsonParser.getJSONFromUrl(url, params);
    Log.e("Some",json.toString());
    return json;
}

public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

public JSONParser() {

}

public JSONObject getJSONFromUrl(String url, List<NameValuePair> params) {

    try {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        httpPost.setEntity(new UrlEncodedFormEntity(params));

        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        is = httpEntity.getContent();
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();
        String line = null;

        while((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }

        is.close();
        json = sb.toString();
        //Log.e("JSON", json);
    } catch (Exception e) {
        //e.printStackTrace();
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    return jObj;
}
}

06-16 17:03:47.890: E/AndroidRuntime(12364): FATAL EXCEPTION: main
06-16 17:03:47.890: E/AndroidRuntime(12364): java.lang.NullPointerException
06-16 17:03:47.890: E/AndroidRuntime(12364):    at com.zafar.login.Camera.fileData(Camera.java:216)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at com.zafar.login.Camera$2.run(Camera.java:186)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at android.os.Handler.handleCallback(Handler.java:587)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at android.os.Looper.loop(Looper.java:130)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at android.app.ActivityThread.main(ActivityThread.java:3691)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at java.lang.reflect.Method.invokeNative(Native Method)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at java.lang.reflect.Method.invoke(Method.java:507)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
06-16 17:03:47.890: E/AndroidRuntime(12364):    at dalvik.system.NativeStart.main(Native Method)
06-16 17:03:55.115: I/Process(12364): Sending signal. PID: 12364 SIG: 9