Parsing JSON data to string in Android app

I connect a database on my server from the Android application and I want to use the info the server send back to me. Here is the response I get from the server :

[{"id":"1","userid":"1159448580","address":"Kishinev 3"}]

Here is my function that is realizing the connection to the server and trying to parse the response :

String checkForUserIdGetBookmarks (String returnString) {
        InputStream is = null;
        String result = "";
        //the userId data to send
        ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
        nameValuePairs.add(new BasicNameValuePair("userId", userId));

        //http post
        try{
            HttpClient httpclient = new DefaultHttpClient();
            HttpPost httppost = new HttpPost(PHP_URL);
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
            HttpResponse response = httpclient.execute(httppost);
            HttpEntity entity = response.getEntity();
            is = entity.getContent();
        } catch(Exception e){
            Log.e("log_tag", "Error in http connection "+e.toString());
        }

        //convert response to string
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            result = sb.toString();
        } catch(Exce开发者_开发技巧ption e) {
            Log.e("log_tag", "Error converting result "+e.toString());
        }

        //parse json data
        try {
            JSONArray jArray = new JSONArray(result);
            for (int i=0; i<jArray.length(); i++) {
                JSONObject json_data = jArray.getJSONObject(i);
                Log.i("log_tag","id: "+json_data.getInt("id")+
                        ", userid: "+json_data.getString("userid")+
                        ", address: "+json_data.getInt("address")
                        );
                //Get an output to the screen
                returnString += "\n\t" + jArray.getJSONObject(i);
            }
        } catch(JSONException e) {
            Log.e("log_tag", "Error parsing data "+e.toString());
        }

        return returnString;
    }

But when I try to show the already converted string it shows an empty string.

/** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
            String returnString = "";
        checkForUserIdGetBookmarks(returnString);
        Toast useridToast = Toast.makeText(getApplicationContext(), returnString, Toast.LENGTH_LONG);
        useridToast.show();

Where would you suggest is my mistake and do you know other way of getting the response from the server into a string which I can use afterwards?

---

Use:

String returnString = checkForUserIdGetBookmarks(); // and declare returnString inside the method

Instead of:

String returnString = "";
checkForUserIdGetBookmarks(returnString);