最近在做一个小程序，期间发现一个有趣儿的功能，生成小程序码，官方api地址：https://developers.weixin.qq.com/miniprogram/dev/api-backend/open-api/qr-code/wxacode.createQRCode.html，现将实现过程贴出来：

1：获取token

//授权（必填）
String grant_type = "client_credential";
//URL
String requestUrl = "https://api.weixin.qq.com/cgi-bin/token?";
String params = "appid=" + Const.MINAPPID + "&secret=" + Const.MINSECRET + "&grant_type=" + grant_type;
//发送请求
JSONObject data = NetUtil.get(requestUrl + params);
return data.getString("access_token");

2：将获取到的图片buffer转为base64

public static String imgBase64(String token, String path, Integer width, String scene, Integer type) {
    RestTemplate rest = new RestTemplate();
    InputStream inputStream = null;
    OutputStream outputStream = null;
    try {
        String url = null;
        if (1 == type) {
            //获取小程序二维码，适用于需要的码数量较少的业务场景
            url = "https://api.weixin.qq.com/cgi-bin/wxaapp/createwxaqrcode?access_token=" + token;

        }
        if (2 == type) {
            //获取小程序码，适用于需要的码数量较少的业务场景
            url = "https://api.weixin.qq.com/wxa/getwxacode?access_token=" + token;
        }
        if (3 == type) {
            //获取小程序码，适用于需要的码数量极多的业务场景。
            url = "https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=" + token;
        }
        Map<String, Object> param = new HashMap<>();
        param.put("path", path);
        param.put("width", width);
        param.put("auto_color", false);
        param.put("scene", scene);
        Map<String, Object> line_color = new HashMap<>();
        line_color.put("r", 0);
        line_color.put("g", 0);
        line_color.put("b", 0);
        param.put("line_color", line_color);
        MultiValueMap<String, String> headers = new LinkedMultiValueMap<>();
        org.springframework.http.HttpEntity requestEntity = new HttpEntity(param, headers);
        ResponseEntity<byte[]> entity = rest.exchange(url, HttpMethod.POST, requestEntity, byte[].class, new Object[0]);
        byte[] result1 = entity.getBody();
        //切记加上"data:image/png;base64,不然会报错"
        return "data:image/png;base64," + Base64.encodeBase64String(result1);

    } catch (Exception e) {
        log.error("调用小程序生成微信永久小程序码URL接口异常", e);
    } finally {
        if (inputStream != null) {
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (outputStream != null) {
            try {
                outputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    return null;
}

3：将获取到的base64转为 MultipartFile

public static MultipartFile base64ToMultipart(String base64) {
    try {
        String[] baseStrs = base64.split(",");

        BASE64Decoder decoder = new BASE64Decoder();
        byte[] b = new byte[0];
        b = decoder.decodeBuffer(baseStrs[1]);

        for (int i = 0; i < b.length; ++i) {
            if (b[i] < 0) {
                b[i] += 256;
            }
        }

        return new BASE64DecodedMultipartFile(b, baseStrs[0]);
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
}

4：将图片传到服务器，并返回带有https的图片路径

5：结果

{
  "success": true,
  "message": "操作成功！",
  "code": 0,
  "result": "https://**/1568880379942.png",
  "timestamp": 1568880230848
}