我的Android应用程序无法通过PHP从mysql获取新数据

Question

我有一个Android应用程序代码，可使用php脚本从mySQL数据库读取数据。第一次正确读取数据。但是，如果我从数据库手动更新数据库中的数据，则该应用程序将显示第一次运行代码时读取的数据。如果我更改了php脚本的网址，则android应用程序代码将能够读取更新的数据。下面是我的android代码，它从php读取数据。

Log.d("parserclass here", json);中的值将始终显示上载php脚本时首次读取的数据。我已经通过使用Internet Explorer或其他Web浏览器尝试从mySQL读取数据来验证php脚本是正确的。

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";
    HttpClient httpClient = new DefaultHttpClient();

    // constructor
    public JSONParser() {

    }

    public void shutdown(){
        httpClient.getConnectionManager().shutdown();
    }

    // function get json from url
    // by making HTTP POST or GET mehtod
    public JSONObject makeHttpRequest(String url, String method,
                                      List<NameValuePair> params) {

        // Making HTTP request
        try {

            // check for request method
            if(method == "POST"){
                // request method is POST
                // defaultHttpClient
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();
                is = httpEntity.getContent();


            }else if(method == "GET"){
                // request method is GET
                String paramString = URLEncodedUtils.format(params, "utf-8");
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);
                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, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
            Log.d("parserclass here", json);
            reader.reset();
        } catch (Exception e) {
            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 JSON String
        return jObj;

    }
}