//如果你得Url能返回json。可以使用以下程式碼。

/**
     * 根據url獲得json
     * @param url
     * @return
     */
    public static String loadJson(String url)  {
        StringBuilder json = new StringBuilder();

        try {
            URL urlObject = new URL(url);
            URLConnection uc  = urlObject.openConnection();
            BufferedReader in = new BufferedReader(new InputStreamReader(uc.getInputStream()));
            String inputLine = null;
            while((inputLine = in.readLine())!=null){
                json.append(inputLine);
            }
            in.close();
        }catch (MalformedURLException e)
        {
            e.printStackTrace();
        }catch (IOException e)
        {
            e.printStackTrace();
        }
        return json.toString();
    }

    /**
     * 將字串json轉換為json格式，並根據key取出value
     * @param url
     * @return
     */
    public static String findKeytoValueFromJson(String url){
        String getJosn = loadJson(url);
        String j1 = "\"";
        String jj = "\\";
        StringBuilder ss = new StringBuilder();
    
        for (int i = 0; i < getJosn.length(); i++) {
            if (j1.equals(String.valueOf(getJosn.charAt(i)))) {
                ss = ss.append(new StringBuilder(jj));
            }
            ss.append(getJosn.charAt(i));
        }
        String jsonStr = ss.toString();
        jsonStr ="["+getJosn+"]";
        JSONArray jkfJson =  JSONArray.fromObject(jsonStr);
        String  accessToken  = jkfJson.getJSONObject(0).get("access_token").toString();
        return accessToken;
    }