生成加密sign

接口请求时，生成sign

/**     * 生成sign     * @param params     * @return     */    public static String sign(MultiValueMap<String, String> params){        List<String> paramsStr = new ArrayList<String>();        for (String key : params.keySet()) {            paramsStr.add(key);        }        Collections.sort(paramsStr);        StringBuilder sb = new StringBuilder();        for (String kk : paramsStr) {            String value = params.get(kk).get(0);            sb.append(value);        }        String signStr=MD5Utils.getMD5(sb.toString()+key);        return signStr;         }