docs: public static String generateMchPayJsRequestJson(String prepay_id, String appId, String key) {
  		String package_ = "prepay_id=" + prepay_id;
  		Map<String, String> map = new LinkedHashMap<String, String>();
  		map.put("appId", appId);
  		map.put("nonceStr", UUID.randomUUID().toString().replace("-", ""));
  		map.put("package", package_);
  		map.put("signType", "MD5");
  		map.put("timeStamp", System.currentTimeMillis() / 1000 + "");
  		String paySign = SignatureUtil.generateSign(map, key);
  		map.put("paySign", paySign);
  		return JsonUtil.toJSONString(map);
  	}