Android PHP POST重音参数失败

我正在一个项目中工作，我们在客户端有一个android应用程序，服务器端正在用PHP管理。客户端应该发送信息到服务器，它应该用包含结果的json来回复。在我们使用一些特殊字符之前，一切都很容易找到，我不知道如何解决这个问题。

我已经验证了Apache和PHP的设置，两者都使用UTF-8作为默认字符集。

我面临的问题越来越多:

1. 我的PHP代码不能自己管理$_POST中的值，当它们包含特殊字符时。在使用它之前，我应该在PHP中使用urldecode()进行解码吗?这些值通过URLEncoder.econde(myvalue，"UTF-8")发送到服务器。参见下面的代码:
我的php代码返回一个json对象。如果对象中没有特殊字符，则一切正常，但如果它包含一些重音或类似的字符，则无法管理该对象。

我的代码

安卓方面

public class HelperClassJSONDownload {
public HelperClassJSONDownload(){
}
// Given a URL, establishes an HttpUrlConnection and retrieves
    // the web page content as a InputStream, which it returns as
    // a string.
    public JSONObject downloadJSON (String myurl,List<NameValuePair> params) {
        InputStream inputStream = null;
        JSONObject jsonObject = null;
        String json = "";
        try {
            URL url = new URL(myurl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10000 /* milliseconds */);
            conn.setConnectTimeout(15000 /* milliseconds */);
            conn.setRequestMethod("POST");
            conn.setDoInput(true);
            conn.setDoOutput(true);//We need it to set parameters
            conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            conn.setRequestProperty("charset", "utf-8");

            //Writer w=new OutputStreamWriter(
            //      conn.getOutputStream(), "UTF-8");
            //w.write(getQuery(params).toString());
            //w.flush();
            //w.close();
            OutputStream os = conn.getOutputStream();
            BufferedWriter writer = new BufferedWriter(
                    new OutputStreamWriter(os, "UTF-8"));
            writer.write(getQuery(params));
            writer.flush();
            writer.close();
            os.close();
            //END SETTING PARAMETERS REQUEST

            // Starts the query 
            conn.connect();
            int response = conn.getResponseCode();
            switch (response){
                case 200:
                case 201:
                     inputStream = conn.getInputStream();
                     BufferedReader reader = new BufferedReader
                             (new InputStreamReader(inputStream,  "UTF-8"), 8);
                     StringBuilder sb = new StringBuilder();
                     String line = null;
                        while ((line = reader.readLine()) != null)
                        {
                            sb.append(line + "'n");
                        }
                        json = sb.toString();
                        jsonObject = new JSONObject(json);
                        return jsonObject;

                default:
                    return null;
                }

        } catch(IOException e){
            return null;
        } catch(JSONException e1){
            return null;
        }finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (Exception e2) {
                    // TODO: handle exception
                }
            } 
        }
    }

    /**
     * This method create the String we will pass with the parameters
     * @param params
     * @return the string used for  for the parameters
     * @throws UnsupportedEncodingException
     */
    private String getQuery(List<NameValuePair> params) throws UnsupportedEncodingException
    {
        StringBuilder result = new StringBuilder();
        boolean first = true;
        for (NameValuePair pair : params)
        {
            if (first)
                first = false;
            else
                result.append("&");
            result.append(URLEncoder.encode(pair.getName(), "UTF-8"));
            result.append("=");
            result.append(URLEncoder.encode(pair.getValue(), "UTF-8"));
        }
        return result.toString();
    }
     }

这是PHP代码，函数generalCheckUserData()检查一些值并比较客户端提供的信息。如果客户端提交了一些特殊字符是无法管理的。例如，如果我们需要比较一个提交的值与一个'，这个函数不起作用，如果($_POST['values'] == )另外，如果json返回包含一些特殊字符，它将不起作用。

我希望这些信息足够了

 public function __construct() {
    $this->response = array("tag" => $this->tag, "success" => 0, "error" => 0);
    if ($this->generalCheckUserData() && (isset($_POST['tag']) && $_POST['tag'] == 'register')){
        $this->registerNewUser($_POST['user_email'], $_POST['user_password_new'], $_POST['user_password_repeat'],
                $_POST['user_first_name'], $_POST['user_last_name_1'], $_POST['user_last_name_2'], $_POST['user_telephone']
                ,$_POST['user_city'], $_POST['user_province'], $_POST['user_postal_code'], $_POST['user_country']);
    } else  {
        //we create an array where to storage the information returned to the client
        $this->response['error'] = 1;
        $this->response['error_type'] = 1;
        $this->response["error_msg"] = $this->mes;
        echo json_encode($this->response);
    }
}