服務端生成小程序二維碼、掃碼可直接進小程序

      分爲兩步、要生成小程序的二維碼，都是調用小程序本身的api

      一、先獲取token

      二、而後再生成二維碼

    官方文檔https://developers.weixin.qq.com/miniprogram/dev/api-backend/open-api/qr-code/wxacode.getUnlimited.html

             HttpGet httpGet = new HttpGet(
                        "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid="
                                + appid + "&secret=" + secret );
                HttpClient httpClient = HttpClients.createDefault();
                HttpResponse res = httpClient.execute(httpGet);
                HttpEntity entity = res.getEntity();
                String result = EntityUtils.toString(entity, "UTF-8");
                JSONObject jsons = JSONObject.fromObject(result);
                String expires_in = jsons.getString("expires_in");
                
                //緩存
                if(Integer.parseInt(expires_in)==7200){
                    //ok
                    String access_token = jsons.getString("access_token");
                    System.out.println("access_token:"+access_token);
                 }

                URL url = new URL("https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token="+access_token);
                    HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                    httpURLConnection.setRequestMethod("POST");// 提交模式
                    // 發送POST請求必須設置以下兩行
                    httpURLConnection.setDoOutput(true);
                    httpURLConnection.setDoInput(true);
                    // 獲取URLConnection對象對應的輸出流
                    PrintWriter printWriter = new PrintWriter(httpURLConnection.getOutputStream());
                 // 發送請求參數
                    JSONObject paramJson = new JSONObject();
                    paramJson.put("scene", "a=1234567890");
                    paramJson.put("page", page);
                    paramJson.put("width", 430);
                    paramJson.put("auto_color", true);
                    printWriter.write(paramJson.toString());
                    // flush輸出流的緩衝
                    printWriter.flush();
                    //開始獲取數據
                     bis = new BufferedInputStream(httpURLConnection.getInputStream());
                     bos = new ByteArrayOutputStream();
                    bos.write(bis);
                     byte[]  bs = bos.toByteArray();
                     printWriter.close();                     bos.close();                     bis.close();